Here's the central issue with the coast: saving 10% of $350k anywhere is a lot easier than saving 20% of $175k in a dirt-poor county in <Alabama, Georgia, South Carolina, Florida, Mississippi, Louisiana>.

Partially, this has to do with the desire to retain your absolute peer tier: if your neighbors have PhDs in Alameda, then you want to live with the PhDs in New Orleans. And the Sliver by the River is still expensive. Same holds in Augusta, Jacksonville, wherever.

Those numbers are way off. Th comparison is saving 25+% of $350k vs 50% of $175k.

And that's assuming your spouse doesn't work.

Also higher quality of life. The spouse wants to move for a reason. I wouldn't live in San Francisco for any amount of money.

Sure but then you need to go for even cheaper housing when you retire. Instead of going from high cost of living to medium cost of living, you end up going from medium cost of living to low cost of living or worse.