Microsoft is publishing this as part of a UWP package, writing it in C++ means it could publish the libraries as a framework package allowing other applications

Microsoft is publishing this as part of a UWP package, writing it in C++ means it could publish the libraries as a framework package allowing other applications to consume it as WinRT components regardless of their implementation language (C++, Rust, C#, JS, etc). Whether this is planned or not I don’t know, but as they are putting this in the App Installer package right now which also has a public API I would not be surprised.