I can see their point, sort of
Allowing 3rd-party apps to take over the core function of the watch would take the design experience away from Apple, and I can see how they wouldn't want that.
More importantly however, I wouldn't WANT a 3rd-party app as the core function of my device. Most apps on the App Store are very scammy, to put it lightly. I don't think Apple wants it's product tarnished by reports of apps popping up on your watch for the latest candy crush or medieval raid game. Or to be tracked.
Biting the hand that feeds IT
