Record companies were in such a hurry to crank out their entire catalogues onto CD that they didn't bother remastering anything. CDs were printed from 4th or 5th generation audio tapes. After 15 years or so when the remastered versions started hitting the shelves, the sound quality was noticeably improved. I never knew there was a rhythm acoustic guitar strumming in the background of the Rolling Stone's Satisfaction until I heard the remastered audio.
Of course, consumers were a little peeved, having bought the same album on LP, 8-track, or cassette and then again on compact disk and were now being told there was a new remastered version.
Yeah, that's an issue. On the other hand, a 'remaster' is more art than science. A lot depends upon the engineer and various assumptions he might make.
I love the fact that if I don't want to, I never have to buy another copy of most of my music, since I never use the original media other than to rip it. I did the same thing with my LP albums back in the day. Most of them were played exactly once on a turntable, and copied to cassette, which was then played to death and beyond. Now, when I get a new disk, I rip it and copy the files across 3 or 4 devices, so I have access to it where ever I want. Absolutely love it.