They waited until there were two established player's in a market big enough for probably 1 and a half. They made sure that anyone with enough interest and disposable income had already got a headset and controllers, then launched. Launched claiming to be something different, which people wouldn't recognise. To make sure every base was covered, they had a bunch of oem's produce indistinguishable hardware to confuse everyone. The samsung headset was the best with slightly better resolition, so obviously it was released last. The Microsoft home thing is half arsed, and a rubbish concept anyway.
The inside-out tracking worked nicely though. They should sell that to Oculus and HTC in the fire sale.