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.

[0]: https://lao.ca.gov/LAOEconTax/Article/Detail/265