For quite a few years the NFL has been narrow-casting to what they imagine their audience will be in the near future. I can't remember the last time the Super Bowl halftime performer was someone who interested me.
All you have to do is look at the Cowboys and Raiders and their fan bases to understand what's going on. Despite protestations to the contrary, neither team is interested in actually winning. They're mainly interested in selling two things: swag and beer. Their fan bases are still made up of legacy fans from the actual glory days of the franchises, but they're literally dying off. In the case of Dallas, you have massive numbers of latinos and blacks in the DFW area who will spend any amount of money on the team, and the Cowboys have legacy fan bases stretching from the Southwest to the deep South and up to parts of Kansas (this is from when they were the only game in town in those places). As for the Raiders, they've created fanbases by (a) moving the team around, and (b) having color schemes and traditions that appeal to latinos, blacks, and biker type dirtbags.
While there are other teams in the league that are interested in actually winning, the league isn't going to make a lot of money from them. Packers fans are rabid, but they're landlocked by other fanbases, and they're generally white people who tend to have other things to think about than football. The Patriots are somewhat of a counterexample, only because they appeal to the entirety of New England, but even then those people tend to have jobs and other things that keep them busy. The Steelers somehow have a massive fan diaspora, but they are very insular, pretty lily-white, and generally poor as hell.
So the league knows that serious teams are going to be in the Super Bowl, because (again) the most marketed teams are not going to be anywhere near there. Moreover, the Super Bowl is generally played in areas where affluent people want to be in February, which is another problem. How do they thread that marketing needle? By putting on halftime shows that appeal to the WOMENFOLK of the young men who tend to buy Cowboys and Raiders gear. That means blacks and latinos, and suddenly Bob's your uncle: they have to have weirdo freaky homoerotic rap and/or spanglish icons in the mix.
That's my .02.
