That’s because every other option is currently hot garbage. Either they don’t do as much or they just fail at what they do.
The only competition even close to Apple is Garmin, but their software is inconsistent and jaggy at times. The key advantage to the Apple Watch, isn't so much what it offers terms of capabilities (Which it does well), but the ease-of-use, band customization and overall fluidity makes it a welcomed transition for those who have never experienced the Apple Watch before.