Do you notice this trend with mulatto sons?
Anyway, It's called overcompensation. The same way a lot of light skinned Blacks with two Black parents feel the need to go above and beyond to prove how problack they are to counter the skepticism that their light skin can sometimes bring.
The thing is, no matter what if you're mixed but don't
look black, you'll be criticized. We can comfortably call a man like Barack Obama black because a klan member won't care who his mother is. He's not going to get a taxi in new york, he can still be told he's resisting arrest and then shot down in the streets and left to die like an animal.
If he was a few shades lighter, had a different nose, lips, and hair tho?
You have to take the good with the bad. It makes no sense that someone can claim some of the few benefits you get for being black, while not getting any of the struggle we face. Mixed people may go extra hard because they
know that they can pass, that they can be seen as a 'safe' black person on some pharrell or common shyt. They know that, but they don't want that. I can respect them for basically hitting offers of white privilege with the

and instead trying to uplift the black community.