My $.02 ...
I'm here by default (& my previous Nokia phones E71, N8, etc).
It's not iOS and the Apple walled garden.
WM10 allows for add on storage (SDcard).
Dislike the expense of an iPhone, plus the Apple elitist ...
It's not Android, which I find cumbersome & rife w holes.
While WM10 has diverged (from WM8 / 8.1), Android is absolutely fractured.
The ability in WM10 to get updates, ongoing.
WM10 is more secure, I open dicey emails on my mobile because of the sandboxing.
... and, I just like it.
The camera got me originally, the ease of access (my elderly MIL has a WinPhone), the flexibility, the (currently evolving) ecosystem.
When my banking apps come, I'll like it more.
Pok?mon Go, not so much.