BlackBerry has always had actual data on what single PKB device size would sell the most. Also the data, on price, features and so forth. It knows internally where the best chance for success with a single PKB device was.
It was the KEYone. That was BlackBerry Limited true last planned and internal device given to BlackBerry Mobile as Hail Mary pass. BlackBerry Limited didn't think it would succeed and BlackBerry Mobile thought it could succeed.
BlackBerry Limited has always known success points and has been pretty good about when to exit. Just look at their executives and the insider trades in retrospect.