Despite being by far the most popular sports league on the continent, the NFL and all of its success have benefitted the owners and the league office more than the players on the field, due to a series of failures by the NFLPA in labor negotiations. For example, the NFL remains the only league of the big four without guaranteed player contracts.
Some fans simply refuse to listen to such matters, pointing only to high salaries, and perhaps it may be greedy to ask for much more. But the bottom line remains that athletes in the other leagues have done a far better job protecting their interests, financial and otherwise.