Chag HaSukkos Needs To Compute

Chag HaShavuos is built on a successful seven week avoda

Seven shavuos per person

Shavuos plurality

Chag HaMatzos requires three matzos under each seder plate

And commendable matza consumption all seven days

Matzos plurality

Chazal suggest all Jews dwell in a singular sukka of unity

שכל ישראל ראויים לשבת בסוכה אחת

And the festival is called Chag HaSukkos

Plurality of mystery