Teachers are required to teach the curriculum. Plain and simple.
That said, you can always sneak in what you want.
I've taught the Harlem renaissance when I was teaching American literature.
I not only teach the poets/authors that everyone reads, but we also go for the more controversial poets/writers/speakers, like Malcolm X and Amiri Baraka. I happen to like controversy.
I teach British literature now so I am seriously limited. But, we do spend time discussing why we are mandated to have a British literature class. We read Othello and spend a good deal of time researching and discussing.
I am also writing a research project over inventors and inventions. But I'm not particularly focusing on race/sex. although that is a consideration when choosing the inventions that the kids can choose from.
I also remember a few years ago that I was criticized on this very forum for teaching "black history" because I wasn't black.
X, it's not always the fault of the teacher. Look at the laws. Because of NO Child Left Behind, some of us, especially the history teachers, are forced to a strict time span of what to teach because of state tests. In Texas, at least over half (and I think it's even more) of the 11th grade history test is based on American history, but very little of that deals with "black history".
Also, our resources are limited. I try to very rarely teach with the literature book and I have that option, because all of my students have been issued laptop computers. But for a normal teacher, you only get the textbook, if you are lucky. Some teachers are left buying everything for their classroom. The majority of my stuff in my classroom is self funded.
My big problem right now is that most of my kids have missed so much school that they don't have the basic knowledge. For example, when we were going over civil rights in the 60's when we read To Kill a Mockingbird, I was debunking the myth that the Civil War was about slavery. At least I was trying. I asked the question "Who freed the slaves" and a response from a high school student was "Martin Luther King".
So before I can get into any real discussion, I have to go back and teach basics.
But, as I said before, I can find a way to integrate almost anything into my curriculum. I think what it comes down to is teachers who either don't know, don't care, or honestly don't have the time.
If I was a parent, and I hate to say this, but I've known too many incompetent people in my field, I wouldn't wait on anyone to teach my kid anything. I'd also raise them to ask questions. The kids that make me a better teacher are the ones who question me. In fact, the only reason I go into the reasoning behind being taught British literature is because I had one student, a young black man, who was very angry and resentful that he was taking a British literature course. It was because of his questions that I started changing the way I presented material.
In any case, I don't think the only "black history" taught is slave related. I do, unfortunately, think that the majority of it is taught in February, which I think sends the wrong message. It's not just black history. It's everyone's history, whether we like it or not. You just need to be very aware who gets to pick and choose what histories are taught.