There was one Voat. When the one Voat goes bust, Voat goes bust. Like any enterprise, it's failure can be attributed, at least in part, to poor management.
There are many Lemmy's. If one Lemmy collapses, another Lemmy can take its place. The individual instances might be less stable than a centralized social media site, like Voat was, but when federated the whole unit is more resilient than centralized social media.
The one problem with this is that most of the content does seem to be pretty centered on only a couple instances (lemmy.world mostly, with some also scattered in beehaw.org, Lemmy.ml, and sh.itjust.works). If one of those goes down, especially lemmy.world, it will cripple this place pretty bad. Maybe if we one day get a way to backup or export user profiles and communities to other instances, but until then, I think this place has a centralization problem brewing as well.