Because they are black they think or call themselves African when they are not.
Ever ask a black guy or gal what country in Africa and they have no idea.
Exactly. I am not big on genealogy, but I am glad some of my relatives are. Thanks to their diligent work, I can carry both sides of the family tree back over 500 years, which ain't much in the genealogical game but is about 350 years further back than can most descendants of slaves. And by tracking back that far, I can tap into national and clan histories stretching back millennia. I can entirely understand that black Americans would like to be able to do the same. It's not the end of the world if you can't access that history, but it's great to recover it if possible.