I think the main reason why developers are dropping support for the Apple Watch is the same behavior Apple showed us when they introduced the 2016 Macbook Pros: they were designing the Watch for themselves and they expected the developers to love them just like they love it. I mean just look how Tim Cook was glowing when he told the audience that you can make phone calls with the watch! Ive was happy that he finally could design something made of gold and they presented the Digital Crown like it was the same breakthrough as the touchscreen or the mouse. They even dedicated one button to communication with other watch owners, unthinkable with the iPhone. They made it and it seems like they meant "here's a revolutionary device only we can build. That was our part, now you have to make apps as great as this product!"
They did that with the Watch, the Apple TV, the TouchBar and they'll do it with the Siri speaker. Introduce it with a killer feature: Watch = crown, Apple TV = App Store & Siri, Touchbar = well, Touchbar, Siri speaker = ???, and then give it minimal attention once they're released.
I mean they still don't know what the main purpose of the watch is. Fitness is more and more emerging as the main purpose, but that is quite new...