The colleges want students to commit by May 1.
Jane Smith commits to College B. College A wants Jane Smith at their school though. They come along after May 1 and offer Jane a lot of money to come to College A. Jane is free to go to College A if she wants to, and she will probably lose her deposit at College B. College A has done nothing wrong.
I haven’t yet heard of this happening, but I am sure it has. Perhaps some athletes have experienced this?