No billionaire wants to live in a bunker for the rest of their life. They want adulation, people fawning over them, etc. They’d also need to continue to receive supplies, fresh food (you think they are going to put up with dried rations?), hookers, travel, etc. If they are cut off they will be no better than Hitler in his bunker.

History has shown when the leadership is corrupt everyone around them follows suit. Stealing whenever they can, abandoning their posts at the first chance, incompetence, security goes to whoever pays them the most, etc.