I think there are significant exceptions to the notion that "gang" is used exclusively for non-whites. E.g. a few years ago the FBI listed Juggalos, i.e. fans of Insane Clown Posse as a "loosely organized gang". Juggalos are predominantly white, lower-middle class. And being so designated had real world consequences for many—especially those who had tattoos, or made extensive social media postings—in terms of not being considered for jobs, or even losing jobs they had b/c employers feared liability of having a "gang member" on the payroll.

Motorcycle clubs, especially one-percenters—who are not all white, of course, but predominantly—are also regarded as gangs by the public & law enforcement.

Aryan Brotherhood & other white prison-based organizations are, again, easily classified as gangs.

Then you have the KKK, Dixie Mafia, Volksfront, WAR, Nazi Lowriders ... to name just a few more. And more, definitely, than just "not all".

I think if young men (& now perhaps more women) of color are forming gangs it's for the same reason Jews, Italians, Irish & other marginalized Europeans formed gangs a hundred years ago. To get a leg up in a society that refuses to share equitably with them.