I'm not really surprised. Android Wear, Tizen, Pebble... other companies laid the groundwork and did the market testing for smartwatches, but haven't matured into a predicable standard. Getting any other smartwatch is still strictly for enthusiasts who do their research and bear with some shortcomings. Then Apple comes out with a more mature device, polished and integrated with the iPhone / MacOS family of devices and geared towards regular consumers, albeit at twice the price.
A luxury item, designed for easy integration with the Apple product line, from a well know (and fanatic-creating) brand will always outsell enthusiast niche items in a fragmented market without unifying brand presence. It's got more to do with marketing and business than quality of the product in question.
That said, it's a very nice watch. Just too expensive for my tastes. But price is largely the reason I'm not an Apple customer to begin with.