It's fukked up because a lot of Nigerian/African fathers do this with their half-American children.
My half American older brother was part of our family until he hit like age 14 and then he started to get into it with my mom, at that point he just chose to live with his mom and siblings on his American side.
But regardless, you're Nigerian breh. Good or bad father, it's in your blood.
I don't think it's an American or nigerian thing as much as its a "I got a new family, they're my priority now".
I know some Nigerian families where the dad divorce the mom and the kids

Nigerians for whatever are quick to say "Ill disown my kids, if they don't make me happy."