See the one thing to remember is that places can be majority one party, but if consistently 60% of voter vote for one party that still means that 40% of the voters vote differently. There's tons of moderates and Republicans in very blue areas and there's tons of moderates and Democrats in red areas. Some of these retirees might be moderates or hold different opinions from where they live. They may even simply be folks who aren't plugged into politics and don't really know or care that much what their neighbors' political opinions are.

I'm overgeneralizing here, but retirees don't work (especially not highly physical jobs that badly require workers rights reform. They might do some independent contracting for the last place they worked as a side gig though!) they don't go to school, they don't have much debt with their home, vehicles and student loans all paid off long ago, they don't rent, they aren't first time home buyers, they aren't raising a family and struggling with the cost of daycare. Retirees are basically just trust fund babies except they spent the last 40 years building their own trust fund. And as people are living longer healthier lives, we're getting retirees who have been retired for 20+ years and are even further disconnected from the needs of those who are still working and raising families

My point is, depending on the person, politics probably isn't a big deal to them when they select a low cost of living area to retire to. And in the south there's tons of 55+ communities and communities intended for retirees that are conveniently built just outside of metro areas to reduce tax burden (because taxes are generally the biggest cost for retirees!)