CD Longevity
I can't speak for everyone else but I still buy CDs for several reasons.
The CD represents a physical backup of the uncompressed audio that I can convert to any format I happen to need at the time. My music collection is currently in MP3 format. I use that in my car, on my phone, and on my PCs. If something were to go catastrophically wrong with my digital copies (Hard drives and Flash drives do fail unfortunately) I can always fall back onto my CDs to make new digital copies. Also if I decide to change from MP3 to a newer better sounding format I have that option without having to try and convert one lossy format to another. Converting from the original lossless CD always produces the best results.
Then there's the issue of control. If my music were linked to an online account of some kind it would mean I never have complete control over my investment. While most companies couldn't get away with anything truly shady, that fact doesn't do much to ensure my purchase would still be usable if the seller went out of business. The recording industry does seem to think it should have some right to control what it's sold to me after the sale. I disagree and I won't put myself in a position where they have the option of denying me my right to listen to the music I've purchased. Even if they promised never to use that power, I just can't accept giving them the power in the first place.
There have been newer physical formats to try and usurp the CD but so far they all seem to have some form of control mechanism in place that gives the seller the power to take my purchase away after the fact. For the most part people know this which is why I think CDs are still selling strong.