The special relationship between Chag ha-Matzot and Chag ha-Sukkot - each a seven day holiday including a chol ha-moed period - is both structurally obvious and halachically axiomatic. The Talmud (Sukkah 27a) invokes the common date - the fifteenth of Tishrei and of Nissan - as the source for the independent obligation (in contrast to the implied prohibition to eat a more substantial, betzah sized, meal outside the Sukkah) to consume at least a kezayit in the sukkah on the first night of the chag, parallel to the mitzvah of ba-erev tochlu matzot on Pesach, though there is no scriptural hint of such a law. Some Rishonim contend that this equation to matzah even overrides the typical sukkah exemptions of mitzaer and possibly also rain (Tosafot, though Rashba and others dispute this)! Indeed, Rama (Orach Chaim 639:3)expands this link to matzah to exclude applying the principle of tosefet kedushah to the mitzvah of sukkah, as well as to demand that the sukkah meal conclude by midnight and that it be in take place in a state of hunger (be-taavah), paralleling matzah requirements. In recording these halachot, Rambam (Hilchot Sukkah 6:7) and Shulchan Aruch explicate the matzah parallel.
Yet, the substantive and structural affinity between these two mitzvot and festivals also magnifies subtle differences that imply that while they are indeed parallels, they are equally foils of one another. Rishonim (Ramban on Torah and Tur, beginning of Hilchot Sukkah and others) were troubled why Sukkot, explicitly tied to the exodus from Egypt (Vayikra 23:43), is only celebrated a half year later. Is it mere coincidence (beyond the suggested explanations for delaying Sukkot) that these two pivotal expressions of kedushat ha-zeman and avodat Hashem divide the year and are also maximally temporally distant from one another? Moreover, is it significant that Sukkot concludes after seven days with a quasi-independent Shmini Azeret, while Pesach terminates on the seventh day with a celebration of keriyat Yam Suf that mutes that theme and does not engender either its own birkat ha-zeman or even whole Hallel?
Let us focus on one curious phenomenon directly related to the fifteenth-fifteenth parallel. Halachists were preoccupied with the intriguing discrepancy highlighted by the Baal ha-Maor (end of Pesachim): why do we continue to recite birkat leishev ba-Sukkah beyond the first evening of Sukkot when only the first kezayit of matzah engenders a birkat ha-mitzvah? Baal ha-Maor's own resolution - that one can avoid matzah (and chametz) consumption during the rest of Pesach, but one inexorably requires a sukkah for sleep during this period, is somewhat enigmatic. Does necessity, including the inability to avoid prohibition, per se justify a berachah which is generally associated with the continued meaningful positive performance of the mitzvah? Does the inevitability to bypass the sukkah perhaps reflect a greater halachic ambition for this halachic institution? Some authorities neutralize Baal ha-Maor's difficulty by positing that matzah consumption beyond the obligatory minimum is merely a neutral reshut, while presence in the sukkah always constitutes a kiyum ha-mitzvah, deserving of a berachah. This perspective still does not explain why the halachic system treated these parallels so differently. Moreover, it is noteworthy that some authorities (Tosafot collections on the Torah, Chizkuni, Gera etc.) conclude that the consumption of matzah shemurah beyond the obligatory quantity and throughout the entire Chag ha-Matzot does constitute a kiyum ha-mitzvah, sharpening the discrepancy regarding the berachah requirement.
We may briefly suggest two overlapping approaches to explain this discrepancy (that may in turn also illuminate other distinctions, as well.)
A survey of the pesukim in Parshat Pinchas delineating the mussafim of the respective holidays demonstrates that while the same mussaf configuration was offered throughout Pesach, different configurations were offered every day of Sukkot. The gemara in Arachin (10a-b) suggests that this discrepancy explains why whole Hallel is recited every day of Sukkot, while it is restricted to the first day of Pesach. The Talmud Yerushalmi (Sukkah 5:1) alternatively attributes this phenomenon to the fact that the mitzvah of lulav was obligatory every day in the Mikdash. Both approaches signify that while the kedushat ha-yom of Pesach is defined by the first day, sukkot's sanctity is expressed independently every day. Indeed, a close examination of the Torah's presentation of these apparently parallel chagim- in Emor, Pinchas, and Reeh demonstrates that Pesach celebrates the fifteenth of Nissan, the actual anniversary of yeziat Mitzrayim, though the celebration continues for seven days, while Sukkot, which is at least half of year from the exodus, focuses on a diffused seven day celebration. [The Netziv in his commentary in the various locations also accentuates these subtleties and raises intriguing questions about the respective chol ha-moed status of each festival.] The discrepancy regarding the continued relevance of the berachah after the initial onset of the festival is consistent with the distinctive characters of these chaggim.
Moreover, it is possibly significant, notwithstanding the common "fifteenth" theme and other parallels, that matzah consumption and sukkah habitation represent contrasting types of mitzvot. Eating matzah constitutes a clearly defined and measured (kezayit, kederech etc.) mitzvah. Its symbolic significance is profound but self-evident. This contrasts sharply, and possibly constitutes an intentional foil to the broader, more amorphous, more expansive mitzvah of yeshivah be-Sukkah - "basukkot teishvu shivat yamim...ki be-sukkot hoshavti..." There is discussion about the core commemoration-celebration itself: sukkot mamash or ananei ha-kavod (or both)! Moreover, the core halachic parameters are disputed and debated, an unusual phenomenon for a biblical imperative. Rif, Rambam (Hilchot Sukkah 6:12, 5,6), Gera (O.H. 639:29), and other authorities actually require a berachah for any and every meaningful activity or time in the sukkah, accentuating the comprehensives of this mitzvah. Rambam even posits that the berachah should precede sitting in the sukkah, as that literal application of the mitzvah already triggers the need to recite a blessing. [See Maggid Mishneh's query why it would not be necessary to recite the berachah prior to even entering the sukkah!] However, even the Tosafists (Berachot 11b, ), Ra'avad (6:12), Shulchan Aruch 639:8) and other poskim who limit the berachah to halachically substantial meal consumption, acknowledge the broader goal and requirement of yeshivah be-Sukkah that is conveyed by the pesukim (above) and nusach ha-berachah - "leishev ba-sukkah". In their view, the focus on substantial meals comes under the rubric of ikkar poter ha-tafel (primary applications include or exempt secondary or peripheral manifestations in berachot). [See the debate between the Magen Avraham and Taz (Orach Chaim 639:8) Even the Taz, who places great emphasis on eating meals acknowledges that one engaged in a taanit would say leishev ba-Sukkah for other activities.] The Talmud's expansive catalogue of activities appropriately to be conducted in the sukkah (28b) are universally accepted.
R' Manoach (on Rambam 6:7) suggests that the broad formulation of "leishev ba-Sukkah", rather than achilah or sheinah (sleeping in the Sukkah) was designed to emphasize the comprehensiveness of this mitzvah. He further suggests that this breadth itself solves the Baal ha-Maor's puzzle regarding the difference between matzah and sukkah! Evidently, R' Manoach conceives the expansive, ambitious portfolio of yeshivah be-Sukkah as reflecting a perspective on the character of this mitzvah that precludes restricting its spiritual significance to the time of its initial and absolute obligation. [See also his remarks on 6:7 regarding the option of reciting a berachah on consumptions that do not absolutely require a sukkah.]
The parallel festivals of Pesach and Sukkot- each an expression of the exodus experience- also constitute two distinctive types commemoration and expression of avodat Hashem. Pesach, the anniversary of yeziat Mizrayim, focuses in a very targeted way on the transformative event itself which effectively changed the historical trajectory and destiny of Klal Yisrael. Its matzah focus is clear and its impact requires a multi-day celebration of that charismatic moment. A birkat ha-mitzvah can only be recited at the critical moment itself. Sukkot, however, addresses the aftermath of the exodus, the cultivation of the enduring relationship between Knesset Yisrael and Hashem. It is the ultimate symbol and celebration not of a single event, but of the enduring relationship, national and personal dependence, and Divine providence- sukkot mamash, and ananei ha-kavod - that Klal Yisrael experienced. While the "fifteenth" theme instructs that intense positive, proactive obligation should initiate the period of commemoration, it is consistent with the sukkot theme that the mitzvah be applied broadly in terms of embracing a range of activities, and that continued immersion in the sukkah environment and experience throughout the entire diffused commemorative period would also generate a birkat ha-mitzvah- "asher kideshanu bemitzvotav vetzivanu leishev ba-Sukkah".