It's also due to the unique conditions under which the Black identity was formed - that is forced colocation, separation from history, and systemic coidentification. Anyone who traces their history back to slavery, which many Black Americans can, basically has to stop there creating one pretty large "sub-group".

There's a case to be made - and some theorists do - that black and Black are different identities in America, the second directly corresponding to that shared loss of history.