The top factor: Lotsa rain - year round. Means the soil is saturated already.
Too much development in too small an area. Lots of soil that would soak up the first couple of inches quickly - covered over with concrete and asphalt.
Geography: Not a lot of topography - but depressions of 4-5 feet, when everything else is flat, are gonna fill quickly.
Building all houses on a mound at least 4' above the highest local street level would alleviate about 80% of the damage that occurs from flooding.
BTW: The soil in NORTH HOUSTON is very sandy - not the clay based soils claimed in the article. Spring (Faux news flooding coverage) is VERY SANDY. Easy to tell - if you see PINE TREES ... it's sandy. Pines don't grow very well at all in heavy clay areas.

Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good ...