East Coast Mutants came from Vault 87 exclusively, or did you overlook the dead Vault Dwellers on gurneys there?
I get this, but that's also not what I'm saying.
I'm saying that the stuff where Bethesda screwed up is that they basically tried to make the East just like the West in, what I consider, to not be a very smooth transition at all. That there are other Super Mutants on the East Coast is already one hell of a coincidence, and then when trying to justify the coincidence, what do you get? "Da mutants have an unexplainable desire to make moar mutants." WTF? Ok so what was once a story of a man trying to unite humanity forcefully is now "herp derp dunno why I do it."
It's not that it's unexplained, it's that the explanations provided make one think "yeah right, my ass...." There's so many incredible coincidences going on that it's hard to take it seriously.
Almost none of this is lore that has been stepped on though. It's just very stupid. That was really the problem with Fallout 3. It wasn't usually that anything in it conflicted with previous lore (although that did happen) it was that what Bethesda chose to do was generally very stupid.
See Lyons' Brotherhood for a good example of this. No lore was technically stepped on in creating Lyons' Brotherhood. It's just a very stupid addition because it made no sense for the Brotherhood to ever want or be capable of launching an expedition to Washington D.C. and it made no sense for Bethesda to do something that stupid when all they wanted was a faction that has next to nothing in common with the actual Brotherhood of Steel in the first place.
Like this. Again, no lore was stepped upon, but the believability of it all is just ridiculous.
Having said that, I actually think Bethesda did a good job with Fallout 3. I mean let's get serious: Fallout 3 was a lose-lose for them. Had they continued on the West Coast, they likely would've screwed up royally and ruined the Core Region forever, something the original fans would
NEVER forgive. Had they done their thing on the East Coast without the Enclave, Brotherhood of Steel, Super Mutants or any other Fallout faction, people would complain it's not Fallout, citing a lack of Fallout faces, complaining that this was just an entirely new game with entirely new factions playing around in a world with fallout elements. So what'd they do? East Coast, but use old familiar fallout faces.
Mind you, it's not perfect. For example, I think it would've been enough to simply have the Enclave moving to the East Coast to start over; after this, there's no need for the Brotherhood of Steel or Super Mutants to be there too. They'd have solved the issue of providing an old familiar face just with the Enclave alone; including the other two just makes the story incredibly hard to believe. Feel free to make their own factions after that. People would complain about the Enclave returning anyways, but yknow what? People were gonna complain, it was a lose-lose situation. I think sacrificing the idea that all of the Enclave died in FO2 for the sake of having a familiar Fallout face appear in FO3 is worth it. It's also not that farfetched to believe the US government would have bases strung all over the US, whereas the BoS going there and the Super Mutants of Vault 87? Those are pretty unbelievable.