Looking through the answers so far, I think the only thing not covered is why not the po white folk or other groups.

The simple answer really is that they aren’t black, because when it comes right down to it, any excuse they found to target black people would have excluded other groups except by accident.

But, that misses out on the other factor. The Appalachians aren’t a hotbed of protest and opposition. Folks up in the hills are too poor, too spread out, and too disconnected from external policies on a national level. There’s simply no need to destabilize those communities because they’re not a problem to the people making laws and decisions.

Same with the asian populations you asked about.

Black folks in cities have an advantage that rural people of any color don’t. Numbers in concentration. Even a minority can be a disruption to oppressors when there’s enough in one place. So keeping that population off balance becomes a priority for oppressors. That it’s black people in the U.S. is largely a matter of detail because the same principle would apply everywhere, with any given minority population being a target where that population group is a potential difficult to enforcing power. Like the rohingya or uyghur peoples as recent examples that were in the news.

Now, being real, black people across the world have been oppressed and abused for hundreds of years. So pretty much anywhere they exist, they get shit on in some way.