And general desirability - diverse and well-paying economy, weather, water, mountains.

Absolutely... though that's harder to point a number to. The "this is how much land is there" is a metric that can't be argued. If you then try to look at the population densities of those areas, it becomes even more clear about why a single family detached house would be that much more expensive.

Houston is more racially diverse than the Bay Area.

It’s also functionality illegal to build anything but single family homes in most of the Bay Area and it’s now out of places to do that. Houston does have more space, but also doesn’t prevent you from building a duplex on your own land.

Pretty much all of the HOAs that are de facto zoning boards of the Houston area would most definitely prevent you from doing anything like that. HOA by-laws are where you'll find the real zoning regulations over there.

I wonder how well those hold up in court if you really wanted to build. I could imagine a Texas court being friendlier to development.

You mean trying to violate the deed restriction with compliance mandated by Section 26-475 (and other applicable places) of the Houston Code of Ordinances? I don't think a lawsuit would hold up very well, unless you could could convince the judge that the city can't regulate land use.

A huge part (half? 1/3?) of the Bay Area is nature reserves of various kinds, but most of that land would be perfectly suitable for housing construction, if it was legalized.

Ok... double the space allocated to the cities and you're still at about 1/3 of the greater Huston area.

Pave every single square foot of the nine counties that make up the Bay Area including Marin, Sonoma, and Napa... and you're still 3,000 square miles short of the greater Huston area.

My disagreement was about "a lot of land that you can't reasonably build a city on". I don't doubt your numbers.

That said, Tokyo, which is a wonderful city to live in, and on more earthquake prone land, has 14 million people on 5,194 square miles: https://en.wikipedia.org/wiki/Tokyo.

Ah yes, bulldoze nature to make it more desirable...

Pretty much all human homes are on on what used to be wild nature.

To me, human homes is one of the most worthy uses of land.