Adding comments doesn't contradict "simple and concise" as it doesn't add much, but on the contrary allows avoiding verbose solutions (repeating names) (but also now you need to do string escaping inside a comment???) such as the one you suggest, which will also not have custom syntax highlighting since it's not part of the spec and have a bunch of other issues (like, now you don't know how many keys you have without parsing every key name to exclude comments)

> If you need additional fields in the json to hold comments

I don't need additonal fields, I need comments

> why not add the fields however you want

Because I can't do that either, there are noticeable limitations