I opened up the Yad today on Hilchos Pesach and was taken aback on Rambam's choice of words for the title : "״הלכות חמץ ומצה. Firstly, why is the Rambam putting the Halachos of the seder (chapters 7 & 8) under this title? And now that Rambam has put them together, doesn't the title sound a drop anti climactic? Like aren't the Mitzvos of Chameitz and Matzah only parts (albeit Mitzvos in and of themselves) of the main Mitzvah of the holiday which is Sippur/Zechiras Yetzias Mitzraim which are performed at the Seder?
He has "Laws of Korban Pesach" in his section on sacrifices. He needed a way to refer to everything else about this holiday. The Torah calls it "Chag HaMatzos" (and in fact, Pesach per se is the 14th of Nissan); so what's most notable about the seven-and-a-half-day period if you take away the sacrifice? No Chametz, yes Matzah.