Like S-expressions don't exist. Or even goddamn JSON. Come on, we don't have to jump from one stupidity (unstructured text) to another (using XML as a data representation format).

CSON or .desktop / .service or something similar is immediately understandable to most people and doesn't waste time with unnecessary tokens like XML does.

Not necessarily. JSON is not bad, _if_ you allow comments. Even plain-jane key/value config files can be sanity-checked. I suspect part of the problem is that anything fancy like that is awkward to do in C, so people take the lazy way out.