Garages are expensive to build and if you design your roads so that no person with the means would choose anything but driving and ignore the rest, then sprawl becomes the reasonable choice, since people are driving to every destination anyway. What’s the point of the added expense of a garage if you don’t really care about being close to other things nearby?

Houston is built on a swamp so you can’t really dig a lot without dealing with humidity, water, etc. Multilevel means investment and debt. It can take many years to break even. You can make $25/hr per space and quickly make profit and sell in 10 years for 10 times what you paid for. There are multi level parking though.

Basically, it’s greed.