That’s another reason against the salary cap/floors without idea: the amount of revenue generated by organizations is vastly different among one another. More than NBA basketball and certainly NFL football, MLB baseball is an intensely local sport with very little national or even regional appeal. Maybe that’s because of the everydayness of the enterprise: to be really tuned in to your team or the league, you have to follow it every day, because the landscape is always changing. Contrast this with football, which stays static and is subject to analysis (over, more likely, overanalysis) for an entire week in between games. So an NFL fan has the luxury of contemplating a lot more teams and players and the league while it is essentially in stasis. I think that might lend itself to maintaining more national profile than baseball.
And, of course, the NFL pools its money to a nearly complete degree, and the Players have a lot more access to how much money is flowing through it, making them far more able to negotiate a fair share of the proceeds in a negotiation of salary caps.