Mainly due to reason #2. Big networks now own a great portion of this country's radio/TV stations. And they pretty much decide what kind of music can be played on-air. As a result, edgy, progressive, experimental musics are being excluded most of the time.

The difference is that in US the foundation of music is very good, so it's going to take a long time to actually "see" the decline. While in Asia, it happens way too fast.