Managed Direct X was replaced by an incompatible XNA, which was dropped on the floor, with the advice to learn C++ and move into DirectXTK.
Silverlight was the app framework for Windows Phone 7 as well, dropped on the floor for Windows Phone 8.
C++/CX was replaced by a junk framework that is basically ATL with a new name, with the same tooling as Visual C++ 6.0 with ATL.
UAP was the percusor for UWP.
The "compatibility story" goes like this. Windows 8 drops all compatibility with former Windows, but WinRT requires rewriting the application three times, for phone, tablet and desktop, due to the API space.
Windows 8.1 improves the situation by introducing UAP, where the views still have to be written three times, but the API space for business logic can be shared. Requires a rewrite from previous WinRT.
Windows 10 introduces UWP, as consolidation of three platforms, requires a rewrite from previous WinRT.
XAML islands get introduced as bridge between Win32 and UWP, a year later plan gets dropped and WinUI 3.0 gets introduced, and Project Reunion.
Yet another year ensues, WinUi is now merged with Project Reunion as the Windows App SDK.
Requires yet another rewrite.
In the middle of this, .NET Native gets dropped, and .NET 6 still doesn't provide the same AOT capabilities.
On the C++ side, a group of devs manages to kill C++/CX without any equivalent tooling, telling everyone complaining that customers should suck it up and wait for the day ISO C++ supports Herb Sutter's metaclasses ideas, so that they don't do any C++ extensions like C++/CX or god forbid Qt and C++ Builder.
Lots of enterprises stuck with .NET Framework use WCF.
As for Azure OS, lets see what the future holds, it isn't the only cloud OS in town.