Why do Americans feel that America is 'the greatest country in the world'?

Perhaps it's subjective, and my personal feeling is that it's anything but 'the greatest country in the world. I live in the US, but things, in general, have deteriorated terribly over the last 30 years. So, to me, that sentiment is only about conceit. There is nothing great about America IMO unless one is a bazillionaire. America offers a low quality of life which has been documented-lowest for a first world nation-and either one can afford or die trying. No one-especially government-cares about the working classes.