The readability and obviousness of XML can not be overstated. JSON is simple and dense (within the limit of text). But look at JSON alone, and all you can do is hope for named fields. Outside of that, you depend on context knowledge and specific structure and naming context.

Whenever I start editing json config files I have to be careful about trailing commas, structure with opening and closing parens, placement and field naming. The best you can do is offer a default-filled config file that already has the full structure.

While XML does not solve all of it, it certainly is more descriptive and more structured, easing many of those pain points.

It's interesting that web tech had XML in the early stages of AJAX, the dynamic web. But in the end, we sent JSON through XMLHttpRequest. JSON won.