New
#1
The problem is the devices. New devices don't come out at the same rate as they do for Android. And MS's partners don't have the clout of Apple where releasing a single new device can have a huge market share.
The OS is good, although those that are in the know are likely waiting for Windows Phone OS 10 now, which can also be contributing.
If I want a Windows Phone, I have to put up with a lower spec device than the most recent Android or iPhone devices on the market right now.