I would love to know how this entire probe started? When people complain about other suspected dirty schools not being named, my suspicion is that this started based on a complaint related to the shoe companies - maybe the IRS noticed some missing money and started snooping around - I mean, Adidas isn't gonna have an account labeled "Money to pay off high school recruits with". That money had to be coming from somewhere not obviously traced, so there is likely a money laundering aspect here.
My guess is that the feds started following the money, and the named schools so far are just the ones that came up in the immediate money trail. I doubt the feds specifically targeted any specific university to start. Once they found there was widespread corruption, they'll start looking further. Hence, tip line, etc...