Why didn't the Master, and by extension, the unity, target Vault City?
One of the more notable pieces of lore to come from fallout two is Richard Moraeu/Gray having been a vault-born, vault eight, specifically. He would live to see the people exit the vault, and be exiled not much longer.
Fast-forward about thirty years, the Master has began forming the basis of the super-mutant army. By another thirty years time, he has more than learnt that Vault-Subjects often produce the best mutants, hence the take-over of Vault 17, and every mutant, even the idiot Harry, having orders to capture pures, that is to say, vaultborn or similar.
So..Gray knows about Vault Eight. It was his home, its possible he spent most of his life there before the mutation. Did he consider them too tainted by life on the wasteland? Was he not the type for revenge? Or would be attacking the nascent Vault City be a move so massive as to alert the rest of New California to super-mutants?