I suspect this is mainly because Windows C++ programmers are the largest group that they feel need convincing. Which isn't totally their fault, Microsoft haven'

I suspect this is mainly because Windows C++ programmers are the largest group that they feel need convincing. Which isn't totally their fault, Microsoft haven't done well by them by not offering good support for UTF-8; you can convert to/from it using WideCharToMultiByte but that's pretty low level, and higher-level APIs like CString will cheerfully munge UTF-8 strings for you. They also tend to conflate Unicode and UTF-16 which again doesn't help less experienced programmers realise that there might be alternatives. I've been through the Windows Unicode stuff at a previous job, which ended up using mostly UTF-16 with some UTF-8 for interfacing to third party libraries and for files which needed to be backward compatible to ASCII (plus significant space savings, which I fought hard for). I think I prefer that approach though, since after the (difficult) conversion you didn't need to worry about encodings in 99% of the code. By their rules you'd gain significant complexity by transforming all over the place in any non-trivial GUI code.