In the same sense I trusted my MP3 downloads on eDonkey before the records association played a foul game.
s/played a foul game/forced me to pay for what I’d been stealing/
FTFY.
There is one reason is that the protocol of storage is open. Doesn't mean the thing can't die obviously, but there is some hope that someone will continue to store the data - there is some incentive (crypto value, however low or unstable that can be) to do that.
Also, nothing stops you from storing the critical data in S3 too. I wouldn't bet what will last longer as a permanent storage.