I blame the full screen calculator App.
First impressions count. The crap full screen calculator Universal App was just one big fcuk up. Unloved, unuseable, it acts as a big red Flag for Universal Apps, what they stood/stand for.
As for Window Phone, I remember spending (what felt like) hours trying to book a UK Travelodge hotel using it, and never suceeded via IE. A colleague bailed me, gave me his iPhone, booked in 5 minutes. Embarassing moment I won't forget in a hurry.
(If Microsoft wanted Business users to use WinPhone devices, these are the things they needed to make sure worked out of the box). The point is, they didn't check and MS paid the price.
Both - Big, big fundamental marketing mistakes.