Thanks to chatGPT there's an infinite supply of Grug wisdom on this specific topic:

Grug see tribe use XML for talk between cave wall. But XML talk too loud. XML say <message>Hello</message>. Why not just say Hello? JSON talk quiet. JSON just say "message": "Hello". Grug like quiet talk.

Grug also see XML not consistent. Sometimes XML use attribute, sometimes use element. Make Grug confused. JSON always use key-value. Grug like consistency.

Grug think XML like big, heavy rock. Hard to carry, hard to use. JSON like small, sharp tool. Easy to carry, easy to use. Grug choose JSON.

It’s good in the shallow style but that’s not exactly why grug would prefer JSON. I think mostly it’s because fewer things can go wrong, and parsers are widely available and always works. Grug would also admit that JSON lacks features (like timestamps), but that the workarounds (number as unix timestamp) works just fine.