It's typical for fan-run fanfiction sites to stay up for years even when the maintainers can no longer update them.

So why is one of the biggest reasons people are excited about An Archive of Our Own the fact that fan sites die all the damn time and they lose their links to their favorite fics?

Some fan-run sites stay up. Many more disappear with no notice when the person who runs it loses interest or throws a fit or can't afford it anymore.