There are other considerations as well. We could probably preserve works for longer if we kept them sealed away in darkness, but we value these works in part because of what we get by experiencing them. What we get out of them as artistic works makes them worth taking such good care of as opposed to just being something that's really really old.
Society wants to see these things, and learn from them, even though every moment they spend out in the open exposes them to more harms.
We're fortunate that digitizing has come such a long way. We can preserve and even recreate a lot of things long after the physical objects themselves are gone. It's not the same as having the originals, but at a certain point the reproductions are all we'll have left.
