Imagine, if you will, the person who is wise to the effect on a floppy disk, but uses a CD instead (Or DVD). They use it a few times but then it too stops working. Why?
Answer:
Repeated clamping between the fridge and the magnet scratches or destroys enough of the metal layer, which is on the label side, to the point that the disc becomes unreadable.
There's also that leaving a disc out in daylight for long enough can destroy its readability, especially if it's a user-written (burned) disc.