Real CDs encode the data as physical pits in the media, which will theoretically last a long time.
CDR and other recordable media encode the data using, among other things, colored dyes in the data layer. These dyes are light sensitive and will tend to fade over time, so you don't expect CDR media to last as long.
These days I copy most of my disks to my computer and then make multiple backups ... before I did this the only "real" CDs that I ever bought that failed were from the Mosaic Art Blakey set, which apparently had some kind of widespread manufacturing problem because I've even tried to buy second copies of that set ... and those disks were bad too.