For one thing, not every place where you might want a comment happens to be in an object.
I cant think of a single example that this would be useful.
(Say you have 15 items in an array. For whatever reason, such as you not being in control of the expected input structure of whatever you're giving this JSON to, you have them grouped with comments at the top of each block.)
You seemed to stop at the for who and for what purpose.
I can 'just' about see the case in something like nodeJS package.json files (that is the least of nodeJS's problems, but that's a whole other conversation). But a readme is a so much better option than having to troll through code comments.
And if that isn't the case for you, not like you don't have the choice.