XAML and C#/C++/VB - there's some nifty features they need to implement in WPF such as virtualizing wrap panel.1. People don't really use apps that much on laptops and desktops.
2. Not a huge mobile market, period.
3. Microsoft's rebooting and lack of support for Windows 10 Mobile isn't really attracting developers and burning existing ones.
4. I don't know about the developer tools so I can't talk about dev friendliness.
Originally posted by flashbaax
One major selling point of UWP is "One App - All deveice (classes)". But currently there is only one deceive class with an attractive reach: Desktop Windows. And this class does need UWP builds.
All other Win10 deceive classes (mobile, hololense, band, xbox) don't exists anymore or are really niche. Exepect XBOX, but no one misses Whatsapp and Snapchat on xbox.