Never's a strong word, seems quite easy to understand why to me. You've got ease of use reasons, historical reasons like the mis-guided Robustness principle, etc.

And these sort of things happen time and time again.

And although officially JSON requires quoted strings, almost none of the parsers actually enforce that, and so you will find a huge amount of JSON out there that is not actually compliant with the official spec.

Just like browsers have huge hacks in them to handle misformed HTML.