[magduf]

I think a lot is just the attitude of those who make and master the music. Back in the 80s, CDs sounded great, but they were sold as being the ultimate in sound quality, and the idea really was that you would keep them at home in their jewel cases and play them on a nice stereo system. Car CD players didn't come until later, in the 90s, and MP3s in the late 90s, and music-playing phones in the 00s.

So I think CDs are now made with the idea that the music is going to be converted to MP3 and listed to on mobile devices, not on nice stereo systems, so they mix them with that target listening environment in mind.