First is marketing. Create a buzz and then don’t deliver the numbers to fill the want.
Second Apple had to scrap a $hitload of them due to a defective piece that fails in short order.
http://www.usatoday.com/story/tech/2015/04/29/apple-watch-component-defective/26593575/
the glorified watch is like the McRib from McD’s. They know they have a winner there so they intentionally withhold the burger a majority of the year.
Limited release
Same reason celebs got first dibs
S