The fact that developers aren't invested in the platform is a big part of why it's living on borrowed time. They can't even get Microsoft developers invested in it; they'd rather develop for iOS first and then Android.
I would say that microsoft supporting iOS and android much better than windows phone is the clearest signal to developers to stay away from windows phone. It's not just windows phone though. They've released office integration for WatchOS, but not for microsoft band. That's what happens when a company transitions from being a platform to being a set of apps and services.
