When there's a lot of things to start with, there's bound to be a lot of things to survive by chance even without preserving. A lot of the stuff that survived was accidentally preserved by nature.

You could say that, but I would point out to its resilience and suitability as a medium for long term information containment. Literally thousands upon thousands have been found. Imagine if one were to try make it last longer :)

With some irony, tablets subjected to the usual destroyer of documents, fire, survive even better as they're vitrified.