Because what liberal is dying to move to the state of Oklahoma? Same reason why Florida and Texas cities aren’t as blue as similar sized cities.
Very few people decide where to move because of the politics of their destination. Lots of liberals have been moving to Austin despite Texas being a red state and young people who want to work in Republican politics move to DC even though Biden got 94% of the vote there. People go where their jobs take them.
I assume they would prefer to live and vote in VA rather than DC.
I think a lot do, but there are non-zero numbers in DC. IIRC the stereotype during the Trump administration was that staffers would live along the north side of the Anacostia, in places like Navy Yard (not that shows up in election results because there, like everywhere, they are wildly outvoted.)