OP's question might seem a bit disingenuous. Though I agree much of black American
pop-art of the last couple of decades has been very subpar, identity obsessive and insistent upon itself, the general question of why black American art focuses so much on black American culture is like asking why 19th century French art is so...
French in scope. They're reflecting the environment they live in, plus the aforementioned publishing incentives to do so which have been elaborated upon by other users here. An ethnic group is naturally going to create art centered around that group and its place relative to the populations around it - not solely, mind, but it's definitely going to be present much of the time.
That being said, it also is deeply unfair to say that black Americans are incapable of creating a wide range of art. Much of American cultural development, particularly in the realm of music, owes itself to primarily Black artists. Yes, the horrendous and toxic lyrical content of certain strands of rap and hip-hop largely developed out of the late 20th-century urban black cultural milieu, though musically it was more heavily influenced by German electronic groups like Kraftwerk - Afrika Bambaataa and the Soul Sonic Force expressed their appreciation of the electronic pioneers from Dusseldorf by sampling their 1976 track
Trans-Europe Express for
Planet Rock in 1982, which is widely credited as one of the first hip-hop tracks. However, before rap and hip-hop, black Americans were instrumental in the development of Gospel (which developed out of old negro plantation spirituals, and still has some residual influences from West Africa such as call-and-response techniques), Ragtime, Bebop, Swing, Jazz, Blues, RnB, Rock n' Roll, Zydeco, Soul, Funk, and Fusion - so there's hardly a dearth of creativity there. When people think of quintessentially 'American' music, outside of Country, Western, Appalachian, American Folk and Bluegrass, or orchestral composers like Aaron Copland or Leonard Bernstein, they usually think of music which was developed primarily by black Americans.
Black Americans also had a strong literary tradition, particularly during the late 19th and early 20th century with figures like Booker T. Washington, Elizabeth Keckley, Paul Lawrence Dunbar, Frances E.W. Harper, Claude McKay, Zora Neale Hurston, Dorothy West, Countee Cullen, Ralph Waldo Ellison, etc. I would argue that it's totally expected that many black American writers at this time would create works exploring their place in the broader American culture. Some of them were born into slavery (Washington and Keckley) and it was still within living memory until around the 1920's. Jim Crow was at its height and black Americans were largely left to their own devices to develop independently, so this also included a lot of existential soul searching.
In terms of visual art, I recommend checking out the works of Henry Ossawa Tanner.
View attachment 3386447
View attachment 3386448
View attachment 3386449
Yeah black American Modern (big M) Art is really ugly because Modern Art is often ugly in general. This has no racial bias. But you also have some really creative projects by contemporary black artists, like the ingenious use of textiles in Bina Butler's work.
View attachment 3386452
View attachment 3386455
View attachment 3386456
As for dance, you need not look past the brilliant artists who came of age during the Harlem Renaissance, and Swing eras. Cab Calloway, the Nicholas Brothers, Bill Bailey, John W. Sublett, Bill Robinson, Alice Whitman etc.
You do not have the broad concept of classic Americana culture without very, very significant contributions by brilliant black American artists in all fields.
Edit: Spelling
