Manton Reece, reacting to stats that David Smith posted of the adoption rate of the Series 3 Apple Watch compared to prior versions:
The big difference between the Apple Watch and the original iPhone or iPad is that many people (perhaps most) do not run third-party apps on the watch. Those people are not even counted in David Smith’s numbers. Unlike the iPhone and iPad, which are significantly improved with new apps, the Apple Watch is pretty good with only the built-in Apple features.
The Apple Watch, as a product, has become very successful, and I know I use mine regularly throughout the day. But it has not been a good platform for third parties. Opening iOS up to third-party developers was instrumental in the success of the iPhone and iPad, but I’ve seen no evidence of a correlating effect between WatchOS and the Apple Watch.
An easy answer to this is that third-party WatchOS apps simply don’t need to exist, but I don’t think that’s the case either. There are plenty of instances where you might want to run a non-Apple app on your watch. I know that I would love to use Transit to know, at a glance or with a voice command, when the next train will arrive. But the platform simply isn’t there yet, and likely won’t be until Apple starts using the same tools as third-party developers.