>>38910857BW isn't responsible for this. If anything, it's its commercial failure that did.
But I have another idea in mind. It was all planned. BW was just meant to introduce some features that would have been harder to accept if they immediately jumped from HGSS to XY. Stuff like linear region, story focus, tons of cutscenes. BW and B2W2 weren't just "the last good games", they were also the "first bad games", they were making sure everyone would get used to the new format. It was all part of their marketing plan.