Recently our department lost one of the best professors who was attracted by a better University. If we were a football club, and he were a leading player, we would receive many millions of compensation.

(a) Why Universities (U) do not sign contracts with best professors (P) similar to contracts with football players? That is, U cannot fire P mid-contract, but P can move to other University mid-contract only for a transfer fee. Long-term contracts of this form would protect P from loosing job mid-contract in countries without tenure, and protect U from loosing best staff. After all, is it fair if U supports a young very talented person, offers reduced teaching load, a lot of money for conferences, etc., in a hope that they will have a Field medallist in 5-10 years, but this person moves to Oxford or Cambridge after first major publications? Note that counterarguments like "this is risky for U because P may start working bad, and unacceptable for P because restricts freedom to move, even for family reasons" applies exactly in the same way to football players as well.

(b) If transfer fee existed, what would be current transfer records? How much would best Universities be ready to pay for, say, Fields medallists?

P.S. I understand that I am not asking specific research-level math question here, but so are many high-voted questions on this website, e.g. When should a supervisor be a co-author? or Have you solved problems in your sleep?