Content-addressed storage and error correcting codes mean that one can make bitrot astronomically unlikely with honestly minimal infra investment.

It's copyright that causes anything to disappear from the web IMO -- torrents never die.

EDIT: I am aware that unseeded torrents do in fact die. But it really doesn't take much to seed a whole hard drive's worth of rarely requested data -- this also detects bitrot and so corrects errors automatically if you're not the only copy.

If you are, there's ECC, as well as making another copy.

There are mitigations in both software and hardware, but most consumer machines, by default, do almost none of that. No ECC RAM, no error correction in the filesystem.