Except MSVC is far ahead of Clang[1] (and leagues ahead of Apple Clang) when it comes to C++ standards conformance.
GCC and clang have those same features, but they avoid including them in their main distribution and instead have experimental/development forks that people can use, opting to include them only when they meet a much higher standard than Microsoft.
Which is extremely frustrating when i reported a very similar issue in 17.4 which was reported as fixed (https://developercommunity.visualstudio.com/t/if-constexprre...), etc.
I try building my code every once in a while against MSVC because it has some useful warnings but am very burn out with code breaking on almost every minor version - I shifted all my serious work to clang+libc++ on windows a few years ago already. E.g. I've reported something like 50+ bugs, internal compiler errors, etc... to MS over the years and only a couple for clang even though I use it much much more.
I feel this is a red herring.
People use AppleClang because it ships with Xcode and is integrated with it. Those who are stuck with Xcode will not choose msvc's support for C++20 as a good enough reason to drop everything.
With Clang, the main differences with MSVC boil down to a couple of minor features that are hardly showstoppers, such as simplifying implicit lambda captures.
Between being able to use clang and all it's tooling and being stuck with msvc, using clang is far above in importance.