How do you know? Are you reading them? If so, you're just exposing them to more of the elements that will degrade them. They were never designed to last forever.
And if you're not reading them regularly, then you'll only find out they've gone bad when it's already too late.
There is a reason why transferring backups to new media is done on the regular by professionals. They know that the only way to make sure the copies are good is to ... well, make copies.
Yes, I took all of them out, played the music discs (some are now in my car), and consolidated the data discs a year or two ago. But it wasn't because the data discs were bad, simply that CDR doesn't have the capacity for today.
One of my old photo/video backups is on 100GB Verbatim Bluray. Don't know about these in the future so I did a parity scan on each of them so errors can be fixed if need be. Also on external HD. Let's check in, in twenty years.
And if you're not reading them regularly, then you'll only find out they've gone bad when it's already too late.
There is a reason why transferring backups to new media is done on the regular by professionals. They know that the only way to make sure the copies are good is to ... well, make copies.