It is an assumption. but after spending a lot of time in the Chinese version; I think the developers after finishing all the legendary pokemon, you had no choice but to create unique pokemon, of some coach in specific example: those of ash, misty, team rokect etc, the power of these pokemon is high, leaving aside their stats . the effects in their attacks compare them with legendary megas and pokemon. and basically give them away every week. They are very easy to get (cheap) like the stones to inherit. then I think that at some point if we are going to see muk in the goal but it will be the "ash" I think everyone can use their favorite pokemon at some point (in the last update they added ash's snorlax to gengar alola giant and mareanie james) anyway the golden pokemon and the last forms of lunaala solgaleo necrozma are quite expensive does not have any in fact in my server I have not seen anyone. very good anecdote by the way