Simple, the original team that made DA:O went off to do other things or was promoted into management where they did well, but couldn't replicate the magic of their OG team.
It already is. Check it out on Nexusmods. I did so late last week and they couldnt even fill 1 row of new mods this week. Even Morrowind still gets that done.
"I'm extra sorry that our lawyer got back to me and said the previous wording we did around the 'all future DLC inclusion' was legally binding and we'd get the pants sued off of us unless we changed course."
This. Look at their recent move against the Smash Bros tournament scene.
Look at their love/hate relationship with Splatoon and how their lies and abuse have killed off a once vibrant community and budding e-sport that at one point had several major tournaments.
The only other chapters are on the east coast, have no desire or ability to contact each other. Hell, the west coast group don't even know the east coast chapters survived, let alone thrived because they seized project purity. And while they made the trek before, the middle of the US after that became Caesar's Legion, 15 years after his fall it would be an impassable wasteland.
The east coast chapters were strong enough in DC to send out squads to Boston, but never anything more than a recon. Its even Bethesda lore in fallout 4 that they dont have the resources to move the Prydwin back to DC.
The NCR can make prewar tanks, power armor and vertibirds; they have a GECK.
Edit: to be clear: the only ending the western brotherhood of steel has to survive is to be absorbed into the NCR.
The western Brotherhood of Steel, at the start of new Vegas, is reduced to One Chapter holed up in One tiny bunker with no vertibirds, no supplies, no manufacturing. They have to send lone scavengers out in the cover of night just to steal enough food to survive.
The battle of Helios One ended the brotherhood as a major player in any capacity. They threw everything they had at the NCR and lost badly.
Trick is it directly counteracts the games. In the year the show happens is the same year new vegas happens. This is after the brotherhood was reduced to cowering in a hidden bunker with zero force projection capability.
The show is great, but its Bethesda fallout, not Fallout.
Its a great show and Im enjoying it despite the massive, glaring world consistency issues.
Like what the hell happened to the NCR?
Or, you know, the lore of all of the games outside of Fallout 3 and 4.
Its painfully clear that Todd is salty that the worst two games in the fallout series are 3 and 4. So he's erasing the pre bethesda games and the best game(that respects the original lore), New Vegas.