There are 134 FBS schools now, and if they have an average roster size of 110, the drop to 105 means 670 less people will be playing next year than this year. There will also be new Freshmen, players from Juco, and players moving up from FCS and Division II, and those players will more than exceed the players having used up their eligibility. Thus, some number of players will be left without a home.
You’re point is valid but your numbers are off a bit. The average roster size is reportedly 128, which means 134 schools will have to trim 23 spots, which is more than 3,000. But I have been told in-season attrition puts it around 2,800.
Many will be walk-ons who could choose to stay at their school instead of moving elsewhere.
I had no idea rosters were that big. That's a lot of people who will be out of the game. Choosing to stay at their school will not save some - there will be many who are told that there is no longer any room for them on the roster. They may try to portal, but many will find no offers.
The sad thing is, why couldn't they have waited one more year? I believe that this is the last year when people on the roster will have Covid years, so after 2025, there will be a double attrition, as people who entered college football in both 2020 and 2021 will use up their eligibility at the same time, which will leave extra spaces.