Lots of low/middle income Californians actually have a higher total tax burden in Texas.[1] And I’d guess that Austin is one of the places where cost of living is highest for Texas, reducing the net quality of life profit.
Also, residential expansion in those two places is a bit of apples and oranges. Bay Area is surrounded by water, mountains, and Open Space Preserve. Austin is surrounded by land, land, and more land; and most of it is flat.
[1] https://www.bloomberg.com/opinion/articles/2021-05-19/wait-c...