Just my own personal experience:
Growing up in predominantly white/hispanic southern oregon, sagging was in fashion while I was in high school from 00-04’, and since we only had white and hispanic/latino kids, it was them doing it.
When I became a teacher for a houston suburb, I discovered the the sagging pants were strictly a black student phenomenon. However! There are a faction of black students who wear ULTRA-TIGHT pants as well. On average, I’d say black students at the school I taught wore normal jeans. That’s the danger of averages, of course.
And teachers would often discuss how odd it is that the phenomenon has survived for so long as well. We had strict rules against it, supposedly, but administrators rarely ever supported it. I sent many kids out of my classroom with sagging pants, only to have it ignored by admins.
Also, the students at my school almost universally started wearing basketball shorts underneath their pants, to get around the “no underwear” showing rule. This looked doubly ridiculous of course, but I was impressed with the ingenuity. Officially, of course, the administration said that wearing shorts underneath sagging pants was still unacceptable, even though wearing shorts by themselves were just fine. So it became obvious to everyone that it was just “the man” trying to oppress the students. I mean, the students knew it was completely illogical, “Why are we allowed to wear basketball shorts, but not sagging pants on top of them? My underwear aren’t showing!”