How come Houston hasn’t elected a Republican mayor in almost 40 years?

While I am aware that the races are on paper “non-partisan” the mayor has a political party usually affiliated already by this point. Did my research and noticed since the early 1980’s mayors of Houston have been always affiliated with the Democratic Party.

While Houston is a blue city and I know you’re going to be commenting that, bluer cities like New York City, San Diego, and Dallas have elected Republican mayors. So what’s the difficulty for Houston in doing this? Also do you think it will happen long term?