>>51254551nta, but the reason is likely due to babies needing a parent to hold an specific item, but also needing a parent to hold a everstone to get the non regional offspring.
Imagine if Mime Jr got a Galarian Form
>Galar breeding center>You put Kanto Mr Mime in>You get Galar Mr Mime because you are in Galar >You put in Kanto Mr Mime with an everstone>You get Kanto Mr Mime because everstone overrides region >You put in Kanto Mr Mime with incense >You get Galar Mime Jr since you are in Galar I guess they could make it so that you get the non-regional baby (Kanto Mr Mime) by having one parent hold the everstone and the other hold the incense, but that might cause some other complications.
