Had UWP run on windows 7 we might have seen some more take-up.
These days it's getting even easier with Xamarin adding support for WPF, but even without that sort of hand-holding there have always been options.
XAML/WPF is much better than "no backwards compatibility" if you needed to support a UWP-first application on Windows 7. Certainly there were more issues moving the other direction, but particularly/mostly if you had skipped architecting for Silverlight as an intermediate step.
Seconded. The previous times I wanted/needed to do Windows development, the first step was ridiculously simple:
BUY book
FROM bookstore
WHERE author = 'Charles Petzold'
AND title CONTAINS 'Programming Windows'
ORDER BY publication_date DESC
LIMIT 1
Nowadays, that gives "Programming Windows Sixth Edition", from 2013, which "focuses exclusively on writing Windows Store applications", for Windows 8, almost always in XAML and C#. He says that "Plenty of other books already exist for writing Win32 desktop applications, including the 5th edition of Programming Windows. I’ll occasionally make reference to Win32 API and desktop applications, but this book is really all about writing new Windows 8 applications".
If I use this book, will it work for Windows 10 also? Are these applications only distributable via the Windows Store or can I host them for download from anywhere? If I want to distribute an application through the Windows Store does it have to be this type, or can I also distribute Win32 desktop applications via the store?
I have one specific application I miss from my old 3rd generation iPad that I have not found a good equivalent for on my Surface Pro 4, and so would like to write it myself, but I have not found a clear explanation of just what my options are, so have not started.