This is pretty simplistic. Biracial means you have claim over 2 races. These folks are victims of white supremacy basically.
Black people dont wanna claim you
White people dont wanna claim you
When you dont wanna claim black, black people wanna claim you
When you dont wanna claim white, they dont care until you become a wealthy then they want you to claim white so you dont do anything for black people.
Ultimately the only reason to tell someone they have no race is to separate them from potential allies. If every mixed person was down to claim their black side, cacs would have a problem with that. And if every mixed person claimed their whatever side, black people would have a problem with at, but act unsurprised.