The NCAA only exists because the member schools want it to. While it is a stand alone non profit organization, all of its rules and regulations are voted on by the school presidents. The NCAA IS the schools.
As such, it has whatever enforcement power the schools give it. There are obviously anti trust concerns, but if the schools agree as a group to abide by a certain set of rules, then its up to the group to enforce those rules.
Are the schools serious about enforcing eligibility rules? Given the changes going on right now, im not sure the answer to that is very clear.