I wouldn't say that most 3Bs are mixed or middle-eastern, but I'd say it seems there is a higher percentage of 3Bs amongst those groups than other ethnicities. I'm Mediterranean/Middle-eastern with 3B hair tending towards 3C at times, and this hair type seems to be pretty common on both sides of my family, particularly the middle-eastern side. Not just within my family actually, but I know a lot of Lebanese with hair like this - a higher percentage it seems than other groups.