Because the contract was based on the "House" ruling that has not been accepted yet by the Parties involved yet. The money in the contract is coming directly from the schools which is contingent on approval of the "House" settlement. Currently schools cannot make direct payments to players.
Do you actually know what the text of the contract says? I don't believe you do. I know I do not. However, I have not been arguing that the contract is iron-clad enforceable. I have only been arguing against your assertion that it is 100% unenforceable.
The language could be set up in many different ways. If it is set up only for Wisconsin to pay him for non-exclusive use of his NIL in broadcasting games, then it would be extremely easy for him to sell his NIL to anyone else also. If it is set up similar to an employment contract, then it would be easy for him to play at Miami but subject him to penalties for breaching the contract and any monetary damages that Wisconsin suffers from him leaving. If it is set up as an assignment of his NIL rights to Wisconsin for two years, then he could leave and play for Miami, but Miami would not be able to use his name, nor allow his image to be broadcast in their games. I doubt the contract is set up as simple as any of these ideas. The actual language would determine if it is enforceable, but I seriously doubt that NCAA rules would have anything to do with whether a contract entered into between an adult and an athletic association is valid or not. It might not be enforceable if it violates federal or Wisconsin labor laws, or maybe even another state's laws if it was signed in another state. To know we would have to have the actual text of the contract and understand all of those laws. I simply don't believe that your boisterous declarations that the NCAA has to power to invalidate contracts between consenting third parties is a valid position.
I think it is interesting that the leverage in college football used to be completely in the hands of the NCAA, the conferences, and the schools. In recent years it has shifted to almost completely in the hands of the athletes. I think many people, and many athletes are forgetting that once you start entering into mutually agreed to contracts, the leverage ends. Both parties, athletic associations and athletes, are then subject to the agreed upon contracts. The athlete can't continue to complain about the -big-bad-system, because they themselves entered into an individual contract.
I have said before that I think the only way the entire system ends up being resolved is when the players collectively bargain with some entity. I don't know that the NCAA will end up being that entity. It might end up being a super-conference, or the P4 and G5 conferences on one or two contracts. It might end up being something that we haven't even considered up to this point. It is the wild West at the moment, and I would argue that it isn't really working very well for either side. Football programs are in a quandary trying to navigate things. Some athletes are making money by using the portal, but some athletes are being left out in the cold. Some kind of mutually agreed to structure would benefit both sides.