Because nothing comes close to the simplicity and utility that was Windows Phone 8. 10 mostly brought Windows on par with iOS and Android functionally, whilst mostly retaining the simplicity and utility of 8. Add their (used to be) industry-leading cameras and there's an insanely compelling reason to not switch, if you're OK not getting and then having all teh appz.

I've played with Android off and on for ages. My girlfriend has always had iPhones, so I've always had a pretty good view of where both operating systems were at.

Neither were compelling, but after my 950XL broke it was time. And while I know how terrible Android is for an 8th go at the same OS, I'm blown away at the low quality bar Google has managed to get the world to accept. It's like Symbian all over again, but this time with touch screens.