Except how do you represent every possible data type without losing fidelity? I made this point in another leaf, but it's worth echoing again. A perfect example of this is Dates. There isn't a defined JSON type for that so we'd be back to basic text parsing again (which will cause anyone who has dealt with parsing dates to recoil in agony).

When you try to ram a one size fits all approach to everything, you end up with abominations like SOAP with XML. I simply don't get the fascination with trying to use the same tool for every job even if it's not applicable.