To bring out your implicit point, use the right tool for the job. For a simple job use JSON, for a complex job use XML (and XML schema, XSLT etc).
Moreover, the existence of XML keeps JSON simple.
Instead of complex needs motivating people to complicate JSON with hacks, they just use the XML stack. Complicating proposals for JSON (like json schema) don't get traction, because their would-be users already have their complicated needs met.
And... enough grey-beards are around to make this point. I will add that before XML, there was CORBA. XML was hailed as simpler, til people added all the bits that were missing. In the bigger picture, I think everyone is waiting for a replacement for the XML stack that really is genuinely simpler - not just reinventing the same hacks on a different base.
I am skeptical it is possible to invent a stack which solves the same set of problems as SOAP but is significantly simpler. (I would love to be proven wrong though!)
Instead of complex needs motivating people to complicate JSON with hacks, they just use the XML stack. Complicating proposals for JSON (like json schema) don't get traction, because their would-be users already have their complicated needs met.
And... enough grey-beards are around to make this point. I will add that before XML, there was CORBA. XML was hailed as simpler, til people added all the bits that were missing. In the bigger picture, I think everyone is waiting for a replacement for the XML stack that really is genuinely simpler - not just reinventing the same hacks on a different base.