Mostly it is a reaction to the over use of XML and how and why in many situations using something other then XML is beneficial. If a large swath of people of start using JSON without thinking about you will probably start seeing a similar reaction extolling the virtues of another format over JSON.

Yes, those are good features.

The trouble was that it was the all-purpose data exchange tool for a long time, and everyone has seen XML put to all sorts of ungodly purposes. If it were invented today, nobody would be bashing it, because it would be less widely used -- the few people who did decide to use it would be putting it to good use, so they would love it. Everyone else would be using something else that was simpler.