>>31802339Because every new family of pokémon this gen was given a new exclusive move, or ability. The sole exceptions being half the Alolan forms, Lycanroc Midnight, and the UBs depending if you count Beast Boost.
They'll go back and redistribute most of them in the next games, they just wanted them to be exclusive right now. Musharna's obviously getting Comatose, its HA is fucking Telepathy right now.
I bet Altaria will get Fluffy too, which'll be nice.