Programmer Humor

They were chucked out because, according to the guy who defined it, people started using them for parsing directives, which hurt interoperability because now you needed to be sure that the parser would both read the comments and interpret them correctly. Suddenly, those comments might make otherwise identical files parse differently. If the whole point is that it's reliable and machine-readable, keeping it to the minimal set of features and not extending it any way whatsoever is a good way to ensure compatibility.

What you can do is define some property for comments. It's not standardised, but you could do stuff like

{
  "//": "This is a common marker for comments",
  "#": "I've never seen that as a property name, so it might be safe?",
  "_comment": "Property names with underscore for technical fields seem common enough as well, and it's semantically explicit about its purpose"
}