Every player on the fringes of a program has to make a choice: stick it out with limited playing time, or maybe on special teams - OR leave the program and look for something different/better. In the end, every player has to make the choice that is best for their situation. On the one hand, there's something to be said for honoring a commitment and hanging in there. On the other hand, it's a tough pill to swallow when you're told that "you're not good enough to be a starter/major contributor." For some players, going to a smaller FBS program or a FCS program may be the better choice. I knew a kid who walked on at Iowa State, sat on the bench for a couple years, then transferred to a D3 school and wound up leading them on a couple of nice playoff runs.
Having said all that, I agree the timing of the transfers is interesting. You would think that, if a player had no future in a program, the coach would prefer to let them know sooner so they could transfer earlier and give the program a chance to replace them on the roster.