I see Vault 13 as a whole as... more interested in self-preservation than being selfless.  Overall, everyone wants the vault to be fine but everyone also wants someone else to make it happen. They’re too comfortable in their day to day vault life, even in the face of impending doom. Buck himself doesn’t even want to go, he only goes because Jacoren reluctantly guilt-trips him into it. And while it’s no easy decision, Jacoren is also more comfortable to send out the closest thing he has to a son instead of risking himself, his position, or the vault experiment.