It also well known that many of the top coaches have their own "bag men" for many years. Those are the guys who pass the money along and add an extra layer of insulation to protect the coaches.
They are people who are not affiliated with the university program. The NCAA has no authority over them and they are not subject to any NCAA rules. The NCAA can't even require them to submit to questioning, and they can't sanction them. Even if proof ever arose of the recruits getting money, there is nothing to tie that money to the school or the coaches, so only the athlete gets into trouble. Most of the time, their names and identities are never are known to the public nor even the highest level administrators at the universities. In the past, the money usually came from boosters of from the coach himself which could be connected to the school. But now the money comes from the shoe companies, and that made it easier to investigate as a federal crime, allowing the FBI to get involved.
That is why this FBI investigation has been so groundbreaking. The FBI was able to pursue and prosecute these people for crimes that the NCAA never could, and they were able to use methods like getting people to cooperate with them, and secretly recording conversations to obtain damning evidence and build their cases against the coaches.