As you said, MS set the bar that apps had to be ported to run in their UWP platform and sold on that way, but nobody really bothered as they could see the down sides.
We were told it was there for lots of good marketing BS reasons about security and cross platform etc - yea, nobody bought that either.
Now we're going to have emulated x86 on ARM - can't see that performing very well. I wonder how they are going to do things like emulate the keyboard and mouse, given that they had, apparently to re-write the whole OS to make that work - or has someone just swept this little issue / marketing BS under the carpet too ?
I expect that many are already writing their apps on other platforms as they can see the writing on the wall for Windows.