The US Government
For the same reasons they're the worst faction IRL
The Brotherhood of Steel.
Bethesda won't let them die and do anything else with the series ⚙️
Yeah, that was my first choice. Could literally be making the most difference in the Wasteland but they decide to be a bunch of isolationist fuckwads instead.
Yeah it's suffering what happens with a lot of IPs once the actual creative force that made the thing popular in the first place is out of the picture. There's no clear, creative vision on where to go with it so you get a churn of content that either is stuck in the same time period or prequels. It ends up turning into a checklist of stuff you have to include with each iteration. Gotta put the Super Mutants and the BoS in FO76 even it doesn't make sense in the lore because THAT'S Fallout.
You see the same thing with Star Trek and Star Wars - Trek is stuck in the TNG timeline and Wars is stuck in the Skywalker era. Even the good slop like Andor is still wedded to the original trilogy.
And it's such a shame! Fallout is such an interesting, fun, setting. Exploring how society might redevelop is a big part of what makes it so great; the near-complete shift from Fallout 1 to Fallout 2, the NCR growing from a town into a nation and the development of Caesar's Legion between Fallout 2 and New Vegas. Having BoS, Enclave, and Super Mutants as a major force in every game diminishes that so much.
The people who made fallout made wasteland and the sequels right? And they have that clockwork revolution game coming out too that looks pretty sick
Raiders in F3 and F4 where they're just video game enemies utterly devoid of context that exist only to be killed.
Worst part of 3 and 4 is how fucking weak the super mutants are. They are supposed to be very similar to someone in power armor, with maybe a bit lower DT. But bethesda just couldn't help themselves and my had to put them fucking everywhere
Until you hit post-game and ridiculous bullet sponge super mutant masters start showing up.
Railroad hands down. They're a minor faction on the level of the Great Khans but considered the fourth major faction in the exact same manner as all the other factions with no care for them being a resistance group and not owning/being a large organized millitary like the other factions. They even have to piggyback off most of the Insitute's quests because 
couldn't be bothered to give them anything. Thankfully there are at least enough mods that you can actually make them feel like a functioning main faction if you want.
If you ment bad as in evil... I... uh... Its kinda obvious.
The Institute because they have no reason to exist and no goals and their methods are stupid
Lol I deliberately became the leader of them just to find out what the fuck was going on only to find out that, nope, we got nothing.
"We're replacing people with androids"
"Why?"
"ionno" 
some days you wake up and want to be a dramatic evil scientist and if you don't have a reason to then you make one up
They seem kinda like Boston dynamics making those stupid robot dogs
No those have an actual point, creating types of robots that don't exist yet.
The Institute is making robots that are less useful than the robots that already exist and are incapable of rebelling, for no reason
Gary
Gary!
Gary?
gaaAAArrryyy!
The rich Brahmin barons who run the ncr
Republic of Dave, obviously
Boomers
Legion, enclave, brotherhood, ncr
That parody of Scientologists from Fallout 2.
Tabletop, DnD, board games, and minecraft. Also Animal Crossing.
3rd International Volunteer Brigade (Hexbear gaming discord)
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