it's part psychological, as opposites attract, and part natural instinct. even in nature a lioness naturally prefers a lion with a darker mane. other species as well animals make mating choices this way as well. for example the male birds are usually more boldly colored to attract the fe-male. its just how it goes. the melanin in our skin is a powerful thing. almost like a super power, lol.
I can't really speak for all black men but I'd imagine if you're gifted with a certain length and girth, then you just naturally have a preference of pocking rather than being poked