Because they are all legendary coaches who have won a national championship and then all decided to hang it up coincidentally when NIL came around.
My post has nothing to do with their ages.
Didn't Coach K make the Final 4 his last year? They could have coached longer but like you said, NIL was probably their final straw.
Coach K got to the FF in '22 and looked haggard all season including missing games because of health reasons.
Look up other legendary coaches and their ages for retirement...it wasn't mid-late 70s.
NIL may have been the final nail but it was likely just time to be done either way.