And the D stands for Desktop, and no platforms other than GNU/Linux, or as I've taken to calling it, Linux, use X for the DE. It is a Linux standard. Specifically, the role the XDG spec plays on Linux is the role that the official documentation plays on Mac and Windows: to define where well-behaved programs should place their files. The consequences of ignoring it on Linux are the same as ignoring the official guidelines on Mac or Windows, as is the Correctness(tm). If you ignore it on Linux, your program is not well-behaved, and if you follow it on Mac and ignore Apple's official guidelines, your program is not well-behaved. Pointing out many instances of bad behavior does not make behavior less bad.
This specifically breaks down on Windows. The purpose of sticking dotfolders in $HOME is because you can't see them so they don't clutter your user folder, but they're also not hard to find. One of three things must be true:
1. The universal value is in them being hidden, so a program should go out of its way to hide them on Windows, and thus have platform specific code, despite not having a platform specific directory.
2. The universal value is in them not requiring platform specific code (other than maybe checking $USERPROFILE instead of $HOME), so a program should not bother hiding them on Windows, despite this resulting in a user folder with more junk folders than meaningful folders.
3. The whole concept doesn't translate very well to Windows, being a Linux standard designed for Linux. Windows software should be written to conform to Windows standards.
The answer is very clearly 3, and it is no great leap from there to notice that Mac is the same way. It is also no great leap to notice that not a single program that stores stuff in ~/.config on Mac pays the least bit of notice to XDG variables. Your declaration of it being a de facto standard falls completely flat on that point alone: well written software hardcodes ~/Library unless XDG_CONFIG_HOME is defined, poorly written software unconditionally hardcodes ~/.config, no Mac software that I have ever seen hardcodes ~/.config but listens to $XDG_CONFIG_HOME. So it is not standard outside of Linux. What is standard for Linux software, especially cross-platform ports of Linux software, is total abject laziness on the subject of well-behavedness.
This specifically breaks down on Windows. The purpose of sticking dotfolders in $HOME is because you can't see them so they don't clutter your user folder, but they're also not hard to find. One of three things must be true:
1. The universal value is in them being hidden, so a program should go out of its way to hide them on Windows, and thus have platform specific code, despite not having a platform specific directory.
2. The universal value is in them not requiring platform specific code (other than maybe checking $USERPROFILE instead of $HOME), so a program should not bother hiding them on Windows, despite this resulting in a user folder with more junk folders than meaningful folders.
3. The whole concept doesn't translate very well to Windows, being a Linux standard designed for Linux. Windows software should be written to conform to Windows standards.
The answer is very clearly 3, and it is no great leap from there to notice that Mac is the same way. It is also no great leap to notice that not a single program that stores stuff in ~/.config on Mac pays the least bit of notice to XDG variables. Your declaration of it being a de facto standard falls completely flat on that point alone: well written software hardcodes ~/Library unless XDG_CONFIG_HOME is defined, poorly written software unconditionally hardcodes ~/.config, no Mac software that I have ever seen hardcodes ~/.config but listens to $XDG_CONFIG_HOME. So it is not standard outside of Linux. What is standard for Linux software, especially cross-platform ports of Linux software, is total abject laziness on the subject of well-behavedness.