And all of them have far worse user experiences than the Apple Watch for that exact reason. The Apple Watch is a platform, not an app. It defines the type of communication iPhone and AW apps can have in ways that provide tightly integrated experiences.
Again, there exists a totally different hardware product Apple could build for Android that runs on Android OS expectations but it wouldn't be an Apple Watch.
Nah. I've used both types of watches and the UX is similar. Both are platforms. You can write an Android app or an iPhone app that communicates directly with a Garmin watch app. It's not a problem and there would be no need for different hardware to make an Apple Watch work fine with Android. It's purely a software limitation.
Just a meta comment, I fully agree with you here, but using the word "nah" (especially as an opener) comes off as very dismissive. My guess is that is not your intention, so I wanted to offer some friendly feedback on it. It may be a regional thing, as where I'm from it usually includes significant body language that clearly shows that it's not a shallow dismissal but rather a "I disagree but not forcefully" or "I'm unconvinced" but in other regions "nah" is used in a mocking way.
Again, there exists a totally different hardware product Apple could build for Android that runs on Android OS expectations but it wouldn't be an Apple Watch.