Because the homes and jobs available in Houston strike a price point that makes sense for certain incomes. Households making $200k+ per year are migrating to California, many from New York. Californians with middle income ($40k-$90k) are migrating to Texas [0].
The number of households between 40k-90k is greater than the over 200k group.
Because they can't afford to live in SF- which is largely constrained by physical barriers to growth.
I do agree anti building regulations are bad and somewhat at fault but it's not an apples to apples comparison by any means.
Rich people want to live on the west coast because it's beautiful and the weather is pretty nice. In fact I wish I could live on the west coast but could no longer afford to once the baby came along and my wife and I decided to go single income.
It's cheaper in Houston because people don't want to live in Houston- at least not nearly to the same degree.