The time difference between Pokemon Emerald and Pokemon D/P were two years, more or less, during that time, we all (should) know that Pokemon decreased in popularity during Gen 3 because no games were released in those years, the reason for this (at least I think) is because of the Console switch, they had to make a game on a whole new system, thus taking longer than usual.
I think that BW2 were place holder games, something for the fans to enjoy, while they worked on R/S/E Remakes (or whatever) on the 3DS.
Ken Sugimori usually works on the big Pokemon games, but he didn't work on BW2, which is strange to me, he was obviously working on some other project thats bigger than this.
What supports my thought is that Ken was the Graphic Designer for the 4th and currently the 5th Gen Pokemon games, all but BW2 of course, and is maybe working with 3DS.
What do you think? Of course this is flawed in many ways, for all we know he could have had family trouble (god forbid) and sat this one out, but I some how have a feeling I'm right.