If you accept a coach’s offer at virtually every school but MIT you are getting something of tremendous value: almost certain admission. The coach wants something from you for this valuable thing, your promise to go to that school and play on the team. This is because he only has a few spots to offer; if one is accepted but the player doesn’t attend, the coach will be in a bind.
Neither party’s promise/support is legally binding, but they are morally and ethically binding. And without that understanding, the recruiting process can not work the way it does, which is generally to the benefit of both players and schools.
You’ve mentioned the University of Chicago. If your son were to accept an offer there, his chances of admission would be 99%, vs MIT’s 30 - 50%. Very different propositions.