There is a difference in doing wrong/cheating and breaking a rule. Everybody knows they cheated, even the NCAA. The problem is if you do not have a specific rule they broke you can't punish them.
The NCAA doesn't want to punish schools, they just want to collect paychecks. After the PSU fiasco I doubt they will ever punish a school without having 100% proof they broke the rule.
What rule did Memphis break after the NCAA cleared Rose to play in college? Because Rose refused to talk to the NCAA, they wiped out a whole season. Didn't the cheats have people that refused to talk as well?