As for why Blackman, it's probably branding. Disney doesn't really release R-rated movies, but now they will own a studio and distributor that does. Disney is probably squeamish about having stuff like Narcos and Dave Chappelle on the "Disney streaming service." ABC is still ABC at the end of the day. Disney may own it, but it's not the Disney Network channel. It's still ye olde ABC.
So this way they can still own and profit from it all without having to brand the adult content as "Walt Disney Presents the hot new streaming show with lots of sex, blood, cursing, and gore!"