For starters, it’s not a UNIX thing. It’s really more a Linux thing. Some Unixes have also adopted it but not enough for someone to argue that someone “should” be using it in reply to an article about Unix more generally.
Secondly, XDG stems from managing desktop applications. Granted there’s no reason it can’t nor shouldn’t be used for CLI tools too. But equally there isn’t any reason why someone needs to use it. And on headless platforms, it makes zero sense to enforce XDG over any other Unix standard.
Lastly, XDG is surprising complicated. Your example of symlinks et al demonstrates just how much additional work you’re doing just to follow XDG here. If you CLI tool doesn’t spew dozens of config files in $HOME then your recommendation isn’t any better than the one in the article.
I really want to like XDG but like many things that originated from Linux, it’s far from an elegant solution to a simple problem and barely supported outside of Linux too. So I can’t blame anyone for deciding not to bother with it for their own personal software on their personal systems.