Tom Brady openly said that one of the top considerations for choosing Tampa was that Florida has no personal income tax. And I imagine that goes for his wife's income as well.
The thing is this: when you're talking about 10% or more of your paycheck taken from you in a place like California, and you're a big bucks player, that is a lot of money that is simply thrown in a dumpster. Even the sales tax on things purchased is super high. Plus the cost of living for things like housing and gas is among the highest in the nation.
If the salary cap was adjusted for high tax/high cost of living states (and it never will be) that's about the only way it could work out as apples for apples no matter what team a player plays for.
On the other hand, there's always been a certain uneven cost of living and taxation from team to team and in every sport. I think it's just that it might have reached that critical level at least in the minds of some of the highest paid players. Certainly not all.
