It kinda makes sense when you consider Johto starters haven't had a dub or a glow-up in years. Kanto are always given preferrential treatment, Hoenn got Megas, Sinnoh were always beloved and got BDSP, Unova is kinda in the same boat but at least Oshawott was in Legends Arceus, and we're likely getting Kalos starters in Z-A too (the rest are too recent).

Last Johto game was HGSS. Cyndaquil already got a nice alternate Typhlosion, so Z-A is a good opportunity for Chikorita and Totodile to get alternate forms or a Mega. They even brought Tepig, so Unova only has Snivy left behind as of now.