> ...which is very strange that MS seems to be continuing to rewrite stuff in it

From what I understand, the thinking is something like:

- There currently aren't any great alternatives for an attractive, touch-friendly, modern-looking UI framework. UWP applications generally feel pretty good to use despite UWP's problems.

- MS already has to support UWP apps forever (once something ships with Windows it's immortal), so they might as well take advantage of that support guarantee.

The Windows team is currently investing heavily in Chromium/Edge/WebView2, but it's still fairly early days. I'd bet good money that within the next 5 years, web UI in some form will fully replace UWP for new first-party development.