Memes

African-American is pretty awkward but it fits the similarly awkward model of Irish-American, Italian-American. The reason those are more specific should be obvious and horrifying - the vast majority of black Americans have little record of their ancestry before cross-Atlantic transportation. It would be nice if Americans just focused on the American part but these labels were often imposed on them from outside before they were adopted as a matter of spiteful pride from inside. Like LGTBQ Pride, St Patrick's Day parades originally had an element of defiance and protest.

It's useful in AAVE though because it is specifically American as opposed to just "black". There are black slang/vernaculars in the Caribbean, Britain and France for example. Some of it bleeds into AAVE/Global English too - e.g. fam, bruv.