Switching to Rust removes a lot of papercuts from dealing with MSVC. These things could be solved in many other ways, so it's not exactly the reason, just something you also get from adopting Rust.

For C programs Windows happens to be the odd one out for lots of things. It's annoying with its unloved C compiler, missing unix-ish headers and tools, string encoding pains, very different packaging story, etc.

So I think the motivation here is they'll solve just that one CRT problem now, and will have fewer Windows problems to worry about later.

I've done that for pngquant. I can build things with Cargo rather than explain to users that `make` may be `mingw32_make`. I can parse options with Rust's getopts, rather than getting bugreports that Visual Studio can't find `getopt.h`. These aren't hard problems. I could have solved all of them, but I don't have to!

It sounds more like they don't want to be stuck using an old version of C++ for writing their fast-path, and would prefer to use Rust, because of the nice features it provides.