Well, true, but a vast majority of them did.
They weren't designed to fail in the sense of killing everybody. Instead each had different parameters like something out of a Twilight Zone episode. Different ethnicites, 1 woman and 99 men, computer equipment designed to break, etc.
There were some Vaults (such as Vault-8, founders of Vault City in FO2) which were "control groups", designed to open X years after the war, the dwellers to use the G.E.C.K. and begin life anew, yadda yadda yadda, just like Vault-Tec's propaganda implied.