The point is that JSON is a data structure, comment is rather unnatural there. It can be added to JSON though, just like an array could be wrapped in an object with a "comment" field. Usually array name serves as a crude comment. Literate programming isn't very popular.
JSON is not a data structure. JSON is a data language. A computer program is a data structure and doesn't need comments, a programming language is a format for a human to read, write, and interact with automated tooling, whoss content is a program, but for the human uses, comments are important.
