As a literal student of history, I have an idea of why this might be the case.
Apart from the Nat Turner revolt, there's very little primary source evidence to draw upon. The slave revolts were a fact, but without the actual voices of the participants, you can't really put them in context. What do they mean? Why did those slaves revolt while others remained subservient? What does that revolt say about slavery in antebellum America, or even America itself? This is a side effect of two things, A: slaves being stripped of their agency and identity, and B: the unwillingness of the slaveholding interests to publicize and document any threats to the social order. This has made it extremely difficult to speak of American slave revolts apart from generalities, and also why even though John Brown was white, he's become the symbol of resistance to slavery. Since he was white, his identity counted more to 19th century America, his words and deeds were seen as an aberration, whereas slaves were seen as naturally uncivilized and savage. The sentiments and prejudices of the past influenced the recording of the deeds of the past, which influences how America currently interprets its past, if that makes sense. It's extremely unjust, but that's the history we've been left with.
This is just my perception, of course, and there are a number of other equally valid interpretations.