“A lot of the ground in many places in the Houston area has a lot of clay content.”
Worse, and as in all big cities, all the concrete on the ground, road, buildings, etc. Water has no place to go but rise up.
The larger issue is much of Houston is barely above sea level and the water table is inches deep.
It’s literally a city built on a swamp.
Better than New Orleans, but mainly only because of better construction practices and giant manmade ravines.