Dude, metal is not worldly, it's predominately white--European, to be more specific. It just is. I never said there aren't blacks (or any other ethnicity) who appreciate or participate in metal, but it's just a matter of fact that blacks make up very little of the phenomenon.
I would guess that after whites, Central and South Americans and Japanese (Boris!) are the ethnicities most active in metal.
Suffocation would have been a better example than the horrible bands you referred to, btw. Or even Tom Morello in RATM.