Because people from countries other than America tend to stereotype Americans as generic, arrogant people who mindlessly wave flags and who join the military so they can get killed by countries they're fighting against. That's a stereotype. In reality, modern America barely has much of its own culture. Things that are barely even cultures, as well as things that are cultures, are considered to need stereotypes by people outside of those cultures.

I consider America boring compared to Japan, from what I've heard about Japan. With things like 2channel being in the media rather than talk about oil prices, celebrities, and the like, less war-mongering, and a westernized but still separate culture, Japan's sure less hatable than America. But both governments are corrupt, though Japan is staying far out of Iraq nowadays and I'm pretty sure it always has.