I don't think D&D dropped the ball. I don't think it ever really tried to pick up the ball to begin with. I only know of a handful fantasy games that have produced pre-colonial sub-Saharan African analogues with anything approaching the breadth/depth that European/Asian settings usually get. Neither one omits the often seen seen African tropes, but they are put into a more nuanced context and not treated as representative of the continent as a whole, or the defining aspects of it.
Nyambe, A 3e supplement.
Spears of the Dawn, an OSR game.
I highly recommend both for anyone interested in introducing some sub-Saharan African elements into their game.
I don't really blame games (or D&D in particular) for not doing more. It's more of a symptom of the ignorance people have about sub-Saharan Africa in general. They don't do much exploring because they don't think there's that much worth exploring that isn't full of uncomfortable stuff like slavery, disease/famine, and violent civil conflict. The opposite tendency is to- whenever referring to the region- get preachy and/or paint an idealized depiction of noble savages/high-tech ancients that's not really any more founded in reality. In either case, the reality, the complexity, the context, etc remains unrecognized.
I wouldn't call it offensive, but it can be a bit disheartening to see a setting clearly went through a bunch of references books when they detailed the dozen(s) of Europe or Asia-inspired land distinguished by a wide variety of landscapes, ethnic groups, nations, traditions, religions, weapons, etc, only to get to African-inspired land and kind of just threw in the towel in favor of a mono-culture.
That said, I'm so starved for content that I'll take whatever I can get. Chult, Gulg, Mwangi expanse, Harborhead, Khinasi? Gimme gimme gimme! I just hope want more (content and quality).