WinRT was technologically terrible (which immediately flows from "no one at Microsoft was actually using it to make anything useful"). But that wasn't even what sunk it - the whole requirements around "of course your WinRT app is going to be in the Microsoft Store^TM its the future" did that. The fucking store is a joke, and those requirements existed solely to boost a bunch of idiots internal careers.
The Windows Store thing was so terrible that I would argue the only good thing that came out of it was that it made Valve/Steam invest in Linux.
I still don't understand why the windows store search sucked so badly. It isn't like they had billions of apps. So why did it suck?
My favorite example of that was when WinRT app .exe files could not be launched from the command line. Only via some Windows Store voodoo dance with approvals, signatures and "security" that made WinRT for developers essentially a dead-on-arrival technology.
I would not be surprised if you still cannot launch a fricking .exe.
Correct for the Windows 8 and 8.1 initial versions, it was already quite good with UWP on Windows 10.
But then they rioted internally to kill C++/CX (the only time they had something comparable to C++ Builder), Project Reunion got announced and misused from the original goal, porting WinRT back into Win32 killed .NET Native as well, most of the key team members left to Amazon and Google, Azure or AI teams, the team is now mostly interns or juniors from Microsoft India, no direction, and is a mess, naturally.
I went from a WinRT advocate, to pointing out devs to stay away from it, this is how bad they treated those that actually believed WinRT could be it.