You can also fill up your class too early and not have room left when higher-rated prospects show interest late in the cycle. Every year, we have recruits showing interest in September-November and people say, "Who are we going to cut from our class to make room for this player?" It works both ways.
Many of the top teams have many recruits commit relatively late.
It doesn't really matter when it "seemed" like, the actual truth is that Kill whenever possible preferred to seek commits from players after they played their senior seasons, in order to gather as much data as possible, confirm previous evaluations, and get in on players who matured later and blew up during their senior seasons. We weren't "looking at the leftovers." Many of our best commits during the Kill era committed in the December-February time frame.