Why is the (Republican party) actively engaged in erasing and (cancelling) African American history?

The short answer is, because they can.

They're working to cancel labor history and stories of class struggle as well. They think that by taking away these narratives the working poor will become docile and compliant and the black population will return to being passive Negroes who accept "their place" in white society.

Exactly. If it doesn't fit the narrative, erase the contradiction.

1. I would also add that their motivation for erasing black history is so that they can make disenfranchising
and dehumanizing Black people today more tolerable.

2. Their motivation is intentional and strategic.

1. Also, controlling that false narrative, would be the building blocks of implementing their desired racist goals.

2. That goal being disenfranchising and dehumanizing black people.

I think their overall motivation is that there is a racist fraction of the population that will support them unconditionally if they take a racist position. At this point, the Republican party is a collection of very specific grievances that each collect a very loyal following. These people are one issue voters and will generally support the party regardless of any other issues as long as their issue is supported. There is no risk to the Republican Party that they will lose their allies over their racist positions, but they can definitely bring in another segment of the population, so they do it.

And they can sell it as 'racism is dead because we're eliminating race!'

Have you MET the Republican Party? What part of pandering to the small White Supremacy base are you confused about?