> trailing commas and comments are not supported
One is „accept a wide array of syntactically malformed input, ill defined, substantially complicating the parser“, the other „accept two trivial extensions to the standard that are widely used and don’t affect the resulting data in any way.“
That's always how it starts. If they're truly trivial the reasoning also cuts the other way. Remove them upstream.
Comments were explicitly disallowed from JSON since the beginning, because they could be used as a side-channel for vendor-specific extension mechanisms and harm interoperability.
In that case they made the right choice, as machines won't be inserting trailing commas or comments in the first place, and the risk of having consuming apps inadvertently accept invalid data would be high otherwise.
But from the perspective of a potentially distributed ecosystem of apps and libraries as employed in practice in modern systems, it's actually harmful to interoperability.
Other libs/services/apps that touch the malformed JSON that this change would accept might be present in the overall system and crash on that data. The risk grows with the more components of the overall system that silently accept malformed data and allow the bad data to make its way deeper before it causes issues.
This is what “fail fast” was meant for, if something is going to cause problems in your system at some point in the future, make that “some point” happen ASAP, so that it is easier to identify and fix the source of the flaw.