| Compression simply raises the average volume level. That's a good thing when the playback will be in a noisy environment or on equipment that can't reproduce a wide dynamic range, like a boombox, a computer or car radio. I think that's one reason why excessive compression has become so popular.
Another reason is that digital technology makes compression easier than ever to apply. I can put a compressor on every track if I want in recording software like Pro Tools whereas in the analog world that would have been prohibitively expensive. | 
