Your casual review conveniently left out trying out the app dev platform, which mostly used frameworks that were completely separate from what first party apps got. When wp7 launched the default blank app in Visual Studio took absurdly long to load and didn't have fancy things like ... wait for it ... sockets. There was some gradual and some big improvement over time, so maybe that is a bit of hyperbole, but it is a fairly representative example of the spirit throughout the lifetime of the product.

My thesis is that even if you wanted to make a very good WP app, you needed to work harder and be more of an expert than if you wanted a decent app on other platforms, and some device capabilities would be off the table. Too many people attribute the lack of apps to the lack of interest, which sure is a big factor, but nobody asks if it was technically feasible to have a large number of decent apps.