I think the grander point is that there is no real 'system CRT' on Windows; as I mentioned, there are multiple entry points each at an appropriate level of abstraction available to both platform and application developers (not that there is a real difference between the two, since platform developers may also write applications like Office). Many Windows platform libraries (WIL, for instance) themselves use UCRT instead of MSVCRT now. The latter exists, but it is by no means and has not ever been by any means the single entry point to the Windows platform, unlike glibc on most desktop Linux distributions.