Admissions IS need blind, the coach is not. It is reasonable that the coach might not (cannot, really) support an athlete who might ultimately walk because they got more money elsewhere.
On the flip side, there are lots of D3 schools (no athletic scholarships) where coaches have a thumb on the scale of merit disbursement.
Athletic commitment is a privilege, not a right. Your son can always discuss “do I have a spot if I get in on my own?” If he wants the coach to carry him through admissions, its not unreasonable for him to have to offer assurance in return.