Though most tools that use "JSON" as the config format actually use some superset of JSON, like JSON5, and do support comments. eslintrc, babelrc, vscode config... pretty much every JS tool configuration apart from package.json.
I don't know why people would prefer that over YAML or others but at least you can actually add comments in them and the reason for their popularity doesn't seem to be baked in parser support because these tools are adding their additional "JSON" parsing anyway.
I have a hard time remembering YAML syntax (am I constructing a list or a dict now? Oh well, better look it up) and I know for a fact that it's not just me. JSON is much simpler.
I even prefer JSON over TOML because JSON is simple. TOML has arbitrary rules like how `table = { foo = bar }` can't be multiline, and all that time you spend debugging your attempts at its nested table syntax, you could've just intuitively nested some dictionaries in JSON.
I don't know why people would prefer that over YAML or others but at least you can actually add comments in them and the reason for their popularity doesn't seem to be baked in parser support because these tools are adding their additional "JSON" parsing anyway.