>>58829430ZA is basically a not-reboot for Kalos. It's a game for newcomers, not for people who played XY, nor longtime fans in general. It's all about repackaging and rebranding Kalos.
Notice how all returning characters, few as they are, are the basically impossible to ignore no matter what and even then they still did away with a few of them like Clemont, Bonnie and Sycamore.
My guess is that instead of trying to revitalize and give the Kalos cast a make-over and breathe new life into them considering how undertilized it was they instead decided to give up on them or thought it was not worth the effort to do that so a completely clean slate was the better choice.
ZA is not a game for Kalos or Gen 6 fans at all.
But hey, at least Leon got mentioned 10 times in the base game while Diantha got like 2. Do you like Leon better than Cynthia yet?