Fixed it for you :tongue:
The west coast brotherhood is dying do to the fact that they only gave a crap about themselves. They even know the fact that they are dying off, yet they are too stubborn to change.
The East Coast Brotherhood are willing to change and have also helped the capital wasteland to get back on its feet.
That really isn't the reason why they are dying, the reason they went to war with the NCR.
And besides, the West coast is much more badass. They aren't cowards like the ECBoS, they know they are going to die if they don't give up their beliefs, but they rather die than do that.
They should die already, though.