Why is Oklahoma City more conservative than other cities its size

[Sol]

Most smaller cities in the south-central part of the country are fairly Republican. Since Oklahoma and Texas are in the south, that means white voters are highly Republican, and that's reinforced by fossil fuel industries and evangelical Protestantism. There are fewer Black voters in most of these cities, which lowers the Democratic floor, and turnout among Latino voters in these places is low due to some people lacking citizenship and various kinds of social marginalization. The result is cities which are well to the right of most similar places in other regions of the country.

Dallas and Houston have this tendency to a lesser extent, but they're still noticeably to the right of other big American cities, with the CSA of both voting for Trump in 2020 despite being extremely large and diverse. Other cities, like Waco, Abilene, Amarillo, Tyler, etc. remain total Republican sweeps. Oklahoma City falls between these two in size and politically, in that it has enough Democratic precincts to draw a Lean R seat, but nevertheless remains a pretty Republican metro area overall.

The only real outliers in this regional pattern are the RGV cities (obviously), Austin (obviously), and San Antonio, which is a bit more Democratic than you'd expect, I assume due to higher citizenship rates from long-standing immigration flows.

[Sol]

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.)