>>32506010There were no Kalos Pokemon with Megas that they could give Ash
They'd have to bring back an old Pokemon, which would take spotlight away from the new ones
And Ash-Greninja was Game Freak's idea anyway, the anime staff just wanted something that would make Ash and Greninja's bond stand out more and asked Game Freak, who are the ones who came up with the "synchro" transformation.
