Comment by e_y_

It's not just a theory. It's well documented that Apple has a bunch of APIs and protocols (like AirPods proprietary low latency wireless instead of Bluetooth, NFC was not allowed until years after Apple Pay) that are not available to 3rd party developers. They will sometimes open things up after they've given their own products years of head start because apparently owning most of the ecosystem and having undying brand loyalty from their users isn't enough.

Actually for many years even to build regular Bluetooth devices that did anything besides audio, you needed to add a special chip (Made for iPhone chip) to your hardware to verify that it was an authorized Apple Accessory. Pebble had one, but any 3rd party apps that wanted to send data to the watch (like Uber app, sports apps, random indie apps) had to get allow listed to communicate with accessory devices like Pebble.