Unless they are very popular books, they will be weeded (thrown out or or sold) in a matter of a few years though. People imagine that libraries are infinite storehouses of material, but except for places like the Library of Congress they really aren't. There is limited storage space, and in order to get new books they need to discard the old ones that were rarely checked out. Even the example of old books on parchment aren't immune to this trend -- the books we have from Ancient Greece or Rome are just the really popular ones that were copied over and over again, and the vast majority of works from those times are lost.

Your local library keeps papyrus scrolls on open stacks? I mean, sure, yes, there are libraries that haves such things (the university I work for does), but generally they will be kept in special boxes and you need to ask nicely to get to see them. And don't get me started about the crapitude of your average new book these days. Personally, I prefer print books too, but lasting forever is not really why.

> 500 year support window

Err, no. Something “existing” is not the same as something being supported. Is the original printer still providing free translations to modern languages? Fixing typos and other mistakes? Adding chapters on a regular basis?

It’s kinda ludicrous to call the fact that a thing didn’t spontaneously disappear “support”.