Tech companies went to texas for tax breaks, not because of local talent. People move for jobs. They also provided relocation stipends when they opened those offices. They literally did exactly what you say is impossible. They brought the people so they could have a workforce.
Low COL states are primarily destinations, but blue ones are more so than red ones. People leaving blue states tend to either be red voters or blue voters moving to other blue states.
Urban counties almost always vote blue, as they tend to have more diverse populations. They’ll continue to do so as new voters join, as young people tend to overwhelmingly vote blue.
Blue voters aren’t moving to the Alabamas, Oklahomas, Iowas etc. they’re moving into what would be considered purple states at best. (And yes, texas is closer to a purple state than a red one now).