Easy:
1. Car Dealerships and their owners make great boosters.
2. You then find a parent or an uncle with a job, and you "sell or lease" them a car. The NCAA doesn't have the legal authority to follow that paper trail. They can't see your Uncle Bill only earns 13 dollars per hour with a 540 credit rating. Uncle Bill then gets the insurance and licensing in his name. Those fees too are easily recouped through a bag man or booster.
3. Uncle Bill then "lends" his ride to his nephew in Tuscaloosa.
Does the NCAA think Bama players are getting tricked out free cars? Sure they do. But they can't prove it, and they have no legal authority to track down Uncle Bill's cash flow.
You should really see how bad this stuff is in College Basketball. Nearly every KU player drives a new Cadillac.