>>33004977You're not supposed to believe that Kukui imports a whole small army of rotom, because it's stated pretty early on in the game that Rotomdexes aren't very common and that there is a pretty limited number of them out there.
As for what stops other trainers from just throwing a ball at it, nothing's explicitly stated but I assume that either there's some part of the pokedex itself that prevents this, or it's considered theft so nobody in the Pokemon world would try it outside of the evil teams. That, or it came in a Pokeball when Kukui imported it.
