Could you imagine hitting a rest api and like 25% of the bytes are comments? lol

Worse than that - people will start tagging "this value is a Date" via comments, and you'll need to parse ad-hoc tags in the comments to decode the data. People already do tagging in-band, but at least it's in-band and you don't have to write a custom parser.

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bmacho 5 hours ago | parent | prev [-]

HTML and JS both have comments, I don't see the problem

	▲	Someone1234 4 hours ago \| parent [-]
		And both are poor interchange formats. When things stay in their lane, there is no "problem." When you try to make an interchange format using a language with too many features, or comments that people abuse to add parsable information (e.g. "type information") then there is a BIG problem.