There are a lot of advantages to LA that offset salary. Lebron could have made just as much outside of LA but he realized he would have many more opportunities outside of basketball in LA
And there are a lot of disadvantages to competing on a level playing field.
At Kentucky, their boosters will make sure the deck is stacked heavily in their favor every single year. In the NBA, personnel decisions are made by the front office. Cal would be very foolish to jump without a huge, long-term contract.