There is a LARGE faction of people who go away after the October games. A signifigant group of people who don't buy tickets after November are local businesses, corporates who use games to host office parties and other functions. Weather turns, a lot of those groups disappear. More of those comped tickets become available. The second group are fams with young kids. Don't want to take kids to cold weather games. Out of town numbers fall off too, based on poor driving conditions. There has also been a signifigant part of Griz nation that simply doesn't care about the playoffs. They attend home games for the pagentry, the tailgates and the beautiful weather. The football on the field is secondary. Seriously, there are people who attend the first three or four regular season games, who then turn around and won't even know the Griz are in the playoffs. Those people couldn't even name more than one or two players on the team. Hence, playoff games drop to 20-23,000. Always been that way, probably always will be.
I too do not like that aspect of Griz' nation. I will never like it or understand it. BUT, having said that, without all of those people I just mentioned, the Griz wouldn't be at the top of FCS attendance every year either. But it will ALWAYS astonish me how 25,971 people show up to watch Panhandle State, but on SENIOR DAY and in the playoffs, they won't come.