Allow me ti define vault tec in the PoV of a overseer, ahem....(picture me reading a book)
Vault Tec Overseer- "Oh...I guess the U.S and China blew eachothers load oeaone another...welp, time to keep thexperiment t going on the LAST FUCKING HUMANS MAYBE ALIVE! Not like hopes and dreams is American, testing to see if a man who is exposed to 2 ounces of sugar per hour does anything is the true American way and valuable information.
Decades later-"Wait, the vault dwellers are beginning to get rowdy because they want something else than sugar per hour? This cannot stand! Shit, we gave them to much individual thought...Security wipe the slate clean! We mustt continue the sugar test!"
Even more decades later-A wastelander opens the vault. But they are shocked. A dead skeleton at the vault gate entrance, but is it covered is a white substance, sugar. The Iverseer used a final contingency plan which was to flood the air vent with powdered sugar was used to sufficate them and those unconcious will undergo treatment and brainwashing. Except the vents didn't stop venting sugar and everyone sufficated tasting sugar in the air.
I just defined Vault tec in my shitty made up fan fiction fo a sugar vault.