Lots of "westerners" think they need a magnum rifle to hunt in their own back yards, too.
I've met plenty of "westerners" who think you absolutely have to have a .300 Magnum at the minimum to cleanly kill a bull elk. I've met some who insist that the .338 Win Mag should be considered minimum.
It's not an "eastern thing," in my view...
"Magnumitis" is just a thing.
Roy Weatherby did his thing in South Gate, California. That's pretty far west compared to, say, Ilion, New York.