It's not about America, it's about TV.
The target audience for TV is people who don't care about what they watch. If people care about what they watch, then they tend to watch shows digitally or on DVD. So it's filled with lowest common denominator stuff.
The only exception is publically funded TV, e.g. the BBC. It's funny because I've noticed that Americans often say they are jealous of British TV, but generally speaking, the only good things on British TV are publically funded. The rest is just as terrible as American TV.