Plenty of apps which use .config use it for everything, caches included. The percentage of apps which fully respect the XDG spec is much lower than the percenta

Plenty of apps which use .config use it for everything, caches included. The percentage of apps which fully respect the XDG spec is much lower than the percentage that use the XDG config dir. And this is to be expected - changing the default config dir is one thing, changing your code to put different kinds of files in different places is much more work.