And if JSON did all of those things the libraries that implemented it would suck as well: the complexity comes from the semantics of what all of those things are and do (schema validation is a complex problem, and that has nothing to do with whether you are validating XML or JSON), not how to parse a silly file format.

Hell: a lot of highly popular languages, to be quite honest for a minute, probably don't even have compliant JSON parsers. The real problem here is cowboy developers who think "oh, JSON/XML/whatever is easy, I can throw one of those together in a few minutes" and then /don't even read the spec/ before committing their project into some poor language's standard library.