The NFL has probably gotten far more money from not having a team in Los Angeles than it ever would have earned from having a team there. Every time a team wants a new stadium it drops hints of LA Bengals, LA Vikings, LA Panthers, LA (fill in just about any other team) and the city officials grab the taxpayers by the ankles and shake them for money. Once LA has a team the threat of having the Portland Panthers just isn't as scary to cities.
(Portland picked because it is the largest metro area other than LA which doesn't have a NFL team in a couple hours' drive).
Baseball used to do this with Tampa Bay. But, I believe “city leaders” are more than happy to give pro teams what they want. Lots of fringe benefits for them.