Yamaha of course know EXACTLY how many XS7's they've sold. And I agree (shock, horror!) that the sales figures for that size may indeed be the lowest of all three. BUT....

IT DOESN'T STOP YAMAHA FROM MAKING IT...

And, I predict pretty confidently (because Yamaha has been making all three sizes of WS's for decades, now) that, although it is the lowest selling size, they will continue to keep making it....

Yamaha are quite content to make keyboards that sell in lesser numbers than 61 versions in other divisions. What is it about the arranger division that prevents them from doing the same? A spine, perhaps?