Manner of speech, as with clothing choices, are based upon social conditioning.
There are regional dialects (or “gay clique” dialects even) that are not at all genetic.
The more listeners emulate the speakers around them, the more they will “sound the same”.
You could do the same “study” in gangbangers and find that the slack tones in their manner of speech are different from someone working on Wall Street too “biyotch”. “idn’t tha so? are’ight?”
Good points. I had a boss who worked with a man for years before the man “came out” as “gay” and left his wife and family. My boss said there was a distinct progression of speech changes when the guy converted.... or should I say, perverted.