It’s a GUI framework evaluation. I would imagine most users of a desktop application with a GUI would be Windows users. It would generally be a little weird to develop a professional product that does not work on Windows (or at least Mac). It’s a lot easier to develop that natively than to cross-compile.
I’ll be honest, I’m not really sure what you’re trying to say, but it sounds like cross-compilation to me? The article mentions several different GUI libraries that require dynamic linking and complicated build scripts, so even if you setup rustc to cross-compile (which isn’t that hard but is an extra unnecessary step for your run-of-the-mill dev who just wants to get paid), getting the build scripts to cross-compile C++ libraries or testing the cross-compiled binaries with dynamically linked libraries is a pain, assuming your build scripts even let you do that.
All of this is avoidable by building from Windows. Or I guess you can not target Windows. That works too, but most businesses won’t see that as an option.