I mean, it takes a pretty dumb billionaire to not realize that when a real crisis hits, you'll be a sitting duck (mostly for your own guards / security), in your fancy bunker or forest ranch.
That's more of a naive plan for your run-of-the-mill rich guy, the lower echelon of "rich". Mere $100M-1Bs.
I always thought Zuck-level money gives you better options, such as building your own loyal community. At least village-sized and quite diverse. Which is what you really need when the shit hits the fan.
But maybe Zuck's building that too? And the bunker only a red herring, a hedge for minor temporary hiccups.