I don’t even think they can publish a d&d game on how most teenage boys play d&d. I know when I was teen they wouldn’t be allowed in public.The issue isn't that "slavery is controversial". It isn't, it's pretty unanimously considered a bad thing. The issue is, parents tend not to consider it appropriate subject matter for the early teens who are Hasbro's core target audience.
It's easy enough to add "R rated content" at home. It's a lot harder to take it out of print books you are buying for your 12 year old child.