I think the thing with gangs in general is that there is something holding them together.
So, where I live, there is a recent resurgence of biker gangs involved in organized crime.
These gangs are almost always completely white, and some are known for being racist (though I think that's not as common any more.) but - it isn't actually race or ethnicity that defines or brings these people together - they aren't a "white" or "European" gang as such. They will include people from lots of different ethnic backgrounds, all mixed in together, based mainly on where they live.
so when they are investigating these groups, ethnicity is not really a factor the police consider, it's not that important as a linking mechanism. And it doesn't explain anything about why these guys end up in biker gangs. There are other factors that seem to draw people in.
With the Asian grooming gangs, ethnicity is an important element, and something that is important for police to consider when trying to understand the organization of the gangs. Cultural beliefs also seem to be a factor in their behaviour.
It's not just a sex thing, or a non-white thing either. Lots of organized crime is run by ethnically defined white groups too, and it's also an important part of how the police understand their organization.