racist adverts?

the oh so politically correct "gremlins" adverts are back. the ones they showed last year, where someone who is poor with maths or reading is shown up and then beats their gremlins with a course.

by politically correct i mean the adverts have a cast of all races. however strangely, only white people have the "lead roll" negative based person with the problem. other colours only ever have the "positive" parts in the adverts.

why is that?