It's all due to the "loudness war":

http://en.wikipedia.org/wiki/Loudness_war

http://spectrum.ieee.org/computing/softwar...

Essentially, mastering engineers over-compress (or 'limit') all the sound on each song so that there are few quiet spots, and very little dynamic range. Often times, they clip the hell out of it too, so all the louder high/low frequencies are chopped right off. The result sounds mashed together, causing listener fatigue and, in the longterm, sheer boredom. But it's all done to make a particular song as 'loud' as the previous one on the radio, mp3 player, etc. All it really does is make the music sound just plain awful.

Furthermore, after all that compression on the mastering end, the songs get played on radio stations that utilize TONS of compression. And fans convert the songs into low-bitrate mp3 files, which compress the songs even more.

But music doesn't have to be so 'loud'. The recently-released Beatles remasters sound amazing. The Abbey Road engineers used very little limiting/compression, to give it a very natural, organic sound. The goal was to make it sound as close to the original analog master as possible. In addition, Apple Corps. and EMI packaged them in very attractive CD digipack sleeves (to make them look more like tiny LPs), and packed the booklets with rare photos and complete liner notes. The result? Millions of copies sold, when everyone is crying that nobody is buying music anymore.

Other artists, such as Bob Dylan, John Mellencamp, Neil Young and Donald Fagan, have been quite vocal about the use of excessive limiting.

There are many, many reasons why music is in a slump right now, and 'piracy' is not even one of the main reasons (how does one explain how Radiohead started selling even more CDs after their stuff was leaked/given away on the internet?). The 'loudness war', though, is a very big reason.

Here's a link that explains more:

http://turnmeup.org /

It explains why most music sucks these days.

You can also see how your favorite bands/albums rate on loudness:

http://www.dr.loudness-war.info/