Nah, there's lots of southerners who have problems with speech comprehension too...........Maybe it just takes them longer to get their thoughts together.
It’s actually several things
Our Anglo Saxon DNA with speech inflection from a certain era
The heat....yes it no doubt slows your brain
Manners....southerners of decent upbringing* regardless of rich or poor consider rudeness and talking over folks or spouting off bad form
Fast speech does not indicate intelligence or wisdom....
*Dixie has sadly seen a rise in dignity-less white trash in recent years which frankly defies comprehension.....Tennessee is eat up with it......Kentucky too......the Deep South and Texas not so much
I doubt I have to explain what I’m talking about to most here