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.

See also: postscript. The document structure extensions being comments always bothered me. I mean surely, surely in a turing complete language there is somewhere to fit document structure information. Adobe: nah, we will jam it in the comments.

https://dn790008.ca.archive.org/0/items/ps-doc-struc-conv-3/...

Reminds me how old versions of .net used to serialize dates as "\/Date(1198908717056)\/".

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

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.