There's also no reason that literally every Disney-owned title shouldn't be put on if they're going to go as far as Deadpool and Logan. Hell, they haven't even put up all Marvel movies and shows on the US version of Disney+ yet. Legion, Cloak and Dagger, Daredevil (2003), Elektra, The New Mutants, Helstrom, M.O.D.O.K., Hit-Monkey. I'd expect Once Upon a Deadpool to be added around the Holidays.
Disney+ in the US is missing so much quality PG-13 stuff never mind R. Just think about the Planet of the Apes franchise as an example, and inexplicably family-friendly films like Maze Runner, Real Steel (very underrated film), and Alita: Battle Angel.