Microsoft has this image problem;
People are fed up in using windows, but it is so ubiquous it is difficult to have an alternative for your computer OS.
Macs are seen as good alternative but perceived to be pricey, even as not always true.
Linux is seen as geeky and difficult, even as not always true.

But phones are not PC's, and there are alternatives.
And when there are alternatives, why would you want windows on your phone??
Of course advertising with multimillion dollar budgets helps a bit, people are always susceptible to advertising but that can only go so far.
Now that Lumia brand is no longer Nokia but fully Microsoft I expect WP sales which were always almost fully Nokia sales to dwindle pretty low...