The Talmud (Arachin 10) asks this question. It answers that since each day of Sukkot has its own unique Korban Musaf (the number of bulls changes each day, cf Numbers 29) then in a certain way each day is its own holiday with its own Hallel, unlike Pesach which has the same Korban Musaf every day (Numbers 28:24) for which one Hallel suffices. See here where R Chaim Soloveitchik is cited as ruling that one needs one Hallel for all the days of Pesach, and if one missed saying it on the first day, he says it on any subsequent day. (Note that adding "half Hallel" on any day is a later custom as a way to mark days which are special but don't have a formal Hallel obligation.)

See too this article on the subject.

The Talmud asks this question. The Yerushalmi (Sukkah 5:1) answers simply that Hallel is read all week on Sukkot due to the ongoing Mitzva of the Lulav (which is taken and waved during Hallel). The Bavli (Arachin 10) answers that since each day of Sukkot has its own unique Korban Musaf (the number of bulls changes each day, cf. Numbers 29) then in a certain way each day is its own holiday with its own Hallel, unlike Pesach which has the same Korban Musaf every day (Numbers 28:24) for which one Hallel suffices. See here where R Chaim Soloveitchik is cited as ruling that one needs one Hallel for all the days of Pesach, and if one missed saying it on the first day, he says it on any subsequent day. (Note that adding "half Hallel" on any day is a later custom as a way to mark days which are special but don't have a formal Hallel obligation.)

See too this article on the subject.

The Talmud (Arachin 10) asks this question. It answers that since each day of Sukkot has its own unique Korban Musaf (the number of bulls changes each day, cf Numbers 29) then in a certain way each day is its own holiday with its own Musaf, unlike Pesach which has the same Korban Musaf every day (Numbers 28:24) for which one Hallel suffices. See here where R Chaim Soloveitchik is cited as ruling that one needs one Hallel for all the days of Pesach, and if one missed saying it on the first day, he says it on any subsequent day. (Note that adding "half Hallel" on any day is a later custom as a way to mark days which are special but don't have a formal Hallel obligation.)

See too this article on the subject.

The Talmud (Arachin 10) asks this question. It answers that since each day of Sukkot has its own unique Korban Musaf (the number of bulls changes each day, cf Numbers 29) then in a certain way each day is its own holiday with its own Hallel, unlike Pesach which has the same Korban Musaf every day (Numbers 28:24) for which one Hallel suffices. See here where R Chaim Soloveitchik is cited as ruling that one needs one Hallel for all the days of Pesach, and if one missed saying it on the first day, he says it on any subsequent day. (Note that adding "half Hallel" on any day is a later custom as a way to mark days which are special but don't have a formal Hallel obligation.)

See too this article on the subject.