... but why? The MSVC backend has been falling far behind LLVM with every release. I understand they want uniformity but IMHO either they catch up or they switch fully to LLVM, if they can
For the same reason a Rust frontend is being developed for GCC.
I'm surprised that COM is still a thing!
After the Longhorn reboot all the .NET based APIs were remade in COM, while WinRT introduced in Windows 8, adds a new base interface, replaces type libraries with .NET metadata, and requires an application identity.