@Troy , you missed one - Lack of interest. It is telling that you say this isn't a new revelation.
Bookselling isn't a nonprofit business. If there's no market or demand for middle-aged black man literary fiction why would a publishing house invest in it? Acquisition editors (even the heterosexual middle-aged black men) are probably asking like I asked "where's the conflict?" "What's the plot?" "Where's the drama?"
Like I mentioned James Patterson has no problem selling his Alex Cross books - and has even franchised the character. Neil Cross got a Simon & Schuster book deal to write 3 tie-in novels for the BBC television character "Detective Chief Inspector John Luther" and it achieved critical acclaim.
So actually Walter Mosley isn't a unicorn but rather a brilliant crime novelist who knows what sells and how to sell it.
By the way, interesting books have longevity. It doesn't matter if the author died 10 years ago or 54 years ago. W.E. B Du Bois' Souls of Black folks is still selling well 115 years after it was first published.
To recap; I've established middle-aged black men aren't invisible. You mentioned Skip Gates was a unicorn but I know of other educators that are quite vocal and sought after when it comes to commenting and having input on this country's narrative. In fact, quite a few have blue ticks on Twitter -so they're easy to find.
I've established that middle-aged black men are also visible in other industries from Astrophysics (I forgot to add Neil deGrasse Tyson) to those middle-aged black American men whose wealth and/or accomplishments are without peer, period. So we know there's no nefarious plot to keep the "black man down"... but rather there are obstacles they must hurdle such as prejudice and surviving the effects of racism to achieve their goals.
So you then transitioned to middle-aged black men are invisible in the literary world, save celebrities.
That article you posted is beautifully written and although I've come to a different conclusion, much respect due to the writer. I agree with him on two points, one:
"Yet, the trends of big publishing are not responsible for the halting of young black male literary voices."
And I agree, no one is replacing literary fiction either - but Hip Hop brought oral storytelling from brink of extinction.
Hip Hop is unique to the black community as is gospel singing. Young black men have found their voice in hip hop and they tell the story their way. If you read Lisa Robinson's cover story "The Gospel According to Kendrick" in Vanity Fair-it speaks to the same conclusion the Pulitzer jury came to about Hip Hop as did your writer Kevin Reeves.
They, however, acknowledged that Hip Hop storytelling isn't a lesser version of literary fiction - it is literary fiction set to music and they awarded Kendrick Lamar's Damn" a Pulitzer in Music (for storytelling) . So in the same vein we can say that 4:44 by JAY Z is literary fiction with a black middle-aged man as the protagonist.
Whew, I'm glad you whittled this "elephant" down to bite-size pieces. Because really, I could have continued to produce examples to the contrary every day.
So now that you stated the real challenge, lets go. Note: I'm an avid reader who doesn't fit into your paradigm. So, maybe you shouldn't assume your aforementioned reasoning is why this:
hasn't come to fruition.
I, for one, simply have no interest in literary fiction and definitely wouldn't read it. I find it's too much like navel-gazing.
Now if your middle-aged black man is a protagonist in a suspense thriller then I'm all over it and I have been for years. But then again, I'm into problem-solving. Most of my interaction with vivid, vibrant middle-aged and black men protagonists have come from white-american men writers (dean koontz, stephen king, neil gaiman, greg iles,et al); and from screenwriters. So I guess, I'm attracted to games of strategy and tactics - and I don't care who is telling the story as long as they got game.
Which is why your writer provides an interesting discourse because damn, I listen to hip hop/rap all-day every day! Hip Hop represents game of life and street credz...
So maybe our literary fiction doesn't look or even read like European literary fiction... Even our YA novels don't look like eurocentric YA novels - Even Kwame Alexander has hit a mark with young readers by giving them books in verse ...Dude is like a rock star with his books - I mean he is literally on tour with a tour bus and everything...AND HE IS A MIDDLE-AGED black man!
So maybe that's the answer to the lack of middle-aged black male voices in literature - maybe they must find theirs.