We were talking about the East being isolated from the Midwest and West, not individual Eastern towns.
It has been a long time since I played but uh... I don't remember any plants except in Harold's glade. I remember it being a big deal for that reason. What wildlife do you mean?
As for the super mutants, they *are* starting to wipe everyone out maybe. But most of the settlements are fortified or have natural defenses, and the invasion starts out weak. It's kinda meta, but in canon terms the super mutants are a growing threat which threatens the survivors, but can't overwhelm the holds just yet.
I don't think there's been any official "isolated" reason. Isolated and "far away" aren't the same thing, there has to be a physical reason preventing people to cross over during 100+ years. I seriously doubt there is some kind of wall or even some sort of impassable radiation between coasts.
I mean, the Brotherhood did. At least one remarkable person did. They're not *absolutely* isolated, it's just an incredibly long and dangerous journey for no clear reward. Explorers did it, but caravans didn't. It'd be like undergoing the Oregon Trail through a wasteland full of mutants, and with no free (useful) land waiting for you.
Does it actually say anywhere there's nothing between the East and West coast worthy of note? Cause New Vegas kinda contradicts that. There's loads of tribes and stuff in the nevada desert, to the east of like a dozen cities from Fallout 1 and 2. And you'd think the East Coast would be the less barren coast.
As for animals, well, anything that isn't human. Molerats, deathclaws, radants, radscorpions, brahmin, those anthropomorphic mudcrabs. They have to eat something that isn't just meat. Else they'd have died out by then. And considering how big they are, they must find a lot of it.
The super mutants are such a growing threat the plot of the game just shoves them aside for the Enclave and never remembers again. That leads me to believe they're more of an afterthought and not really the cause of anything in particular. Plus, as I said, just about none of the settlements look ready for a behemoth. Like it'd walk all over Megaton, Tenpenny, The Republic of Dave, that one dumb town with the super heroes, the shacks on the highway, Little Lamplight, etc..
Megaton wasn't ready for my stupid ass at level 2 when I just started shooting everyone.
Keep mind that this "100 years" some people think is sufficient to rebuild civilization, that is only like, max, 3 generations. How much can you get done in 3 generations of Banished? Because that is generally the level of technology most people have to work with.
Some people, like Vault City or New Vegas, had surviving technology to give them a kickstart
200. It's 200 years. And places like Shady Sands were built 100 years after the war.
EDIT: And there's like a dozen vaults all around. Don't tell me they were too stupid to grab a GECK out of one of them.