I was thinking of the origin, not someone who grows up around an accent that already exists.
We pronounce it that way here in Washington state, USA, too.
I female comedian from Boston did a bit about this many years ago. She explained it as if telling a bedtime story to a small child. It was a story about how the lettah R was feeling left out and unwelcome in Boston, and so it got mad and flew away. It flew and flew and flew all ovah the country until it saw Texas, whereupon it dove down and landed in the middle of the word “warsh”
Though most people here in Washington say it with no R (the exceptions tend to be immigrants from the Southern US and their descendents), there are a surprising number of people here who put an “S” in the middle of Leavenworth (pronouncing it “Leavensworth”). I don’t get that one at all.
We used to live in Westminster when I was very little. Even though I don’t remember it, I still cringe when I hear people say ‘West Minister’. (And I used to work with a girl who’d get upset if anyone used the Spanish pronunciation of San Pedro – and she’s Hispanic.)
4 sibs (1945, 1947, 1949, 1953) grew up in Dayton OH until 1961, moved to southern IN.
Youngest, and only youngest, says “warsh” - neither parent (1 central OH farm kid, other SW OH farm kid) used it.
I’ve also heard it in the Ozarks, fwiw - I consider it a “hillbilly” pronunciation (nothing wrong with being a hillbilly ('lessn you have a choice, of course )
My grandmother (raised in rural Nebraska; RIP) ‘warshed’ her clothes. She also had a great deal of trouble with the melting pot:
She would serve pasta with a can of par-MEE-zhen cheese.
She would make tacos out of tor-TILL-uhs.
But my absolute favorite? That big thing in the living room with cushions wasn’t a ‘couch’ or a ‘sofa,’ it was a davenport. Never in my life have I heard anyone else use that term.