There is a reason that the Super Bowl is in New Jersey in February instead of sunny San Diego. San Diego voters will not vot vote for another public built football stadium so the NFL (besides not so subtly whispering that LA needs a team) harrumphs about lack of hotel rooms, transit problems etc......
Extortion plain and simple.
A pretty idle threat, since L.A.'s not going to build them a stadium, either. They've been trying for at least fifteen years, but there's simply no support for spending a dime of government money for another sports team.