The expanded Lumia portfolio that now encompasses every segment is to blame, and the slew of top-notch flagships Nokia has churned out, bringing the amazing 41 MP PureView camera to the Windows Phone world. Its only hindrance was Microsoft's inability (or unwillingness) to introduce new features to WP and pour big bucks in it...
Source: http://www.phonearena.com/news/Nokia-moved-a-record-8-million-Lumias-last-quarter-says-WSJ_id48498
Source: http://www.phonearena.com/news/Nokia-moved-a-record-8-million-Lumias-last-quarter-says-WSJ_id48498