NFL cheerleaders serve many purposes. In addition to lining the sidelines in order to remind the male fans watching men tackling other men for hours that they're not gay, they also make their respective teams cash. Lots of cash.
Next week's Super Bowl will feature the Pittsburgh Steelers and the Green Bay Packers, two of the NFL's six teams that don't have their own cheerleading squads.
While cheerleaders are paid extremely shittily ($100 per game) and are pumped for revenue by the teams they represent. In recent years, teams have turned to the online Lonely Enthusiastic Masturbating Sports Fan demographic to make money, creating subscription-only services wherein fans can view various galleries of the athletic supporters. The Indianapolis Colts even allow fans to order pictures of the cheerleaders. Other teams collect money from cheerleader appearances and product endorsements.
It seems pretty skeevy of the organizations to take advantage of the cheerleaders in the way that it sounds like they do. However, women aren't dumb and it's entirely possible that cheerleaders are doing it for the love of the game.