So they were working on X and Y before BW2 were even released. For all of the other releases, they started work on the next games within two months of the release of the previous one.
XY: October 2013, ORAS starts production "before December" 2013.
ORAS: November 2014, SM starts production "before February" 2015.
So what most people already assumed anyway, for the newer games. I guess a lot of people figured they were working on SM while they made ORAS which was why ORAS was so lackluster.
>>33559926USUM is going to have been the shortest in a long while, maybe since BW2, but it's also the first time in a long while that we've gone back to the same region in the next installment. They shouldn't need as much time.