Why wont my girlfriend's son diversify and expand his taste in women?

he looks all afro american. he is mixed race but noone is going to know that when they meet him. why cant he date women from several ethnic back grounds? why is he so exclusive. he has had a different girlfriend for 3 out of the last 4 fridays and they were all white girls from the local highschool here in neoga. his mother is curious but i dont care as much however she did put the question to me.