Sounds like wishful thinking
I work in an environment where everyone shows everyone else the latest technology, the latest must-have apps, and the customers are very tech-savvy.
I've never seen a WinPhone owner show off some cool app to everyone. I've never heard anyone say it's an absolute delight. What I do hear is how people just wanted a phone, and didn't care what OS it had, but if they could do it again, they'd buy an Android or iPhone.
People who I thought would be long-time Blackberry users ended up switching, but not to WinPhone or iPhone as I would have thought - almost always to Android.
The epic failure of bluetooth in Lollipop 5.0.2 aside, today's Android phones work pretty slick. With an ever-increasing hatred for Microsoft, it will be difficult for them to get the numbers they're anticipating. That's why it's not called guaranteed. Making millions of phones and selling them to dealers is not the same thing as getting them into the hands of customers, and Microsoft will find that latter part very difficult.
Meanwhile customers that are already using android or iphone have probably amassed a bunch of paid apps they really enjoy, and won't want to re-purchase for a different platform. If not for that point alone, maybe they just don't want to mess with a winning formula - if it ain't broke, don't fix it by switching to a platform you're not familiar with. As stats go - many other people aren't familiar with either.