I don't know why he doesn't just say it directly, but all media has an expiration date. It was only intended to last so long (because any longer was too expensive) and floppies are not all past their expiration dates.
This is a good reminder that 'backups' doesn't mean 'put it on a disk and forget it'. You have to maintain them.
The point of the post wasn't to talk about the general aspects of media, but to specifically and directly make a call to action for a subset of all media that I and a team of volunteers can rescue data from.
Baked clay tablets, like stone inscriptions, are exceptional. The records of the past are largely gone.
Unbaked clay tablets tend to simply disintegrate. Those at Knossos and Ninevah were baked by fires that destroyed the buildings in which they were housed. Mycenean tablets appear to have been reused each year, so the 'expiration date' in that case was man-made rather than imposed by the material.
Papyri have also survived more by good fortune than by design, being preserved in tombs and rubbish heaps. They lay undisturbed in an environment where the temperature and moisture content of the air remained stable over time, in a range conducive to the survival of the material.
This is a good reminder that 'backups' doesn't mean 'put it on a disk and forget it'. You have to maintain them.