But then you wouldn't have a secure and well-supplied sanctuary to hide in once the bounty hunters start gunning for the player character and the people of the Wasteland become aware of who you are (since no one in the Wasteland, except for the folks of Vault City, knew where Vault 13 was).
Sure, you lose it in the end once you're kicked out but until then, I can argue you're saving the Vault for your own benefit if you are playing an evil character.
