For me, that "some reason" is normally the overlap between children and parameters:

    <foo bar="123" baz="456"><qux>789</qux></foo>

There's not a great round-trip mapping of that to JSON, like:

    {"foo": {"bar": 123, "baz": "456", "children": {"qux": 789}}}

(which also illustrates why I dislike XML being untyped unless you have a schema file to interpret it with).