Well, JSON is used in a serious way, in fact I doubt you can use most web applications (and many desktop apps too) without your machine parsing some json. And... https://www.json.org/license.html
That license does not cover the JSON spec; nearly all JSON parsers are not distributed under that license. I assume Crockford's original reference implementation of a JSON parser is released under that license, and not much else.
But JSON isn't software, it's just a specification. Any text that matches the specification is JSON, whether it is binary, a string, printed on a piece of printer paper, etc. So what does this license mean, exactly?