It also doesn't help that a lot of the Vaults have *stupid* experiments, especially those from Fallout 3 and 4, and particularly the Penny Arcade ones which are apparently canon for some reason. A lot of the Bible Vaults were dumb too, like Vault 12's door thing is still silly to me.
Vault-Tec would have come off a lot more believable as a corporation/government contractor if the experiments made sense, whether cruel or not. Less "3 people and a panther" vaults and more "Intentionally divide the Vault between red and blue to simulate political factionalism", "lets stuff the vault to twice capacity and make every family a different ethnic group" and so on. Instead, they're a wacky corporation doing cartoonishly evil things for...money? Apparently, the video game equivalent of a Family Guy cutaway gag about Amazon is a scathing anti-capitalist critique.
Also, for what it's worth, I always felt like Vault-Tec and especially West Tek was more a critique of the Military Industrial Complex, not private megacorporations. Like, it's more a Lockheed Martin or Boeing situation than Disney or Amazon. Vault-Tec said it was building vaults to protect people from nuclear warfare, and it took that mandate as free reign to experiment on the people it protected for humanity's long term benefit. West Tek was meant to cure a disease and some shit happened, and they create a super soldier program out of it. That shit wasn't done out of corporate greed, it was done to serve American interests.