>>53008146This is more to do with how mega evolution was only for Pokémon from previous generations.
Your Kalos starters don't mega evolve, but these Kanto starters do!
In X/Y, only Pokémon from generations 1 through 4 could mega evolve, with exception to Diancie, the only gen 6 Pokemon to mega evolve.
OR/AS would introduce more mega evolutions, which included Audino, the only generation 5 Pokemon to feature a mega evolution.
OR/AS also introduced mega evolutions for Sceptile and Swampert, but not Blaziken which was given that privilege in X/Y; particularly as a launch window mystery gift including a hidden ability Torchic and holding Blazikenite.