It's not "lefties" it's "people." There's just more of them. More people, more problems, more compounding of problems. Doesn't matter what your political ideology is. Most people would rather live in a place with civil liberties than one that enforces religious dogma through law and enacts hate against non-whites, non-straight, and women in policy. So they tend to overcrowd the few places where they can have those liberties.

The people who believe in those things but don't like the overcrowding then move. Other like-minded people then follow. Over time, their destination becomes attractive to enough people it starts to face the same overcrowding problems.

Solution is to enact civil liberty policies and unwind religious dogma from law everywhere so future generations in the currently unattractive less-populated areas won't grow up so bigoted. Then there's no need to have places like Seattle get so overcrowded.