The practical one is that state schools are arms of the state. Given that their governor sits on the Board of Regents, I'm not sure they're effectively distinguishable in the way you suggest.
The theoretical one is that universities are not like "every job". The whole point of universities is to encourage bold intellectual inquiry. Academic freedom is at the heart of what universities do. Whether or not they can legally get away with trying to treat professors like serfs seems less important to me.