I'm not sure now that I think about it, but I find this more explicit and somehow more free than json. Which can't be true, since you can just

{"anything you want":{...}}

But still, this:

<my_custom_tag>
<this> 
<that>
<roflmao>
...

is all valid.

You can more closely approximate the logical structure of whatever you're doing without leaving the internal logic of the... syntax?

<car>
<tyre> air, <valve>closed</valve>  </tyre>
<tyre> air, <valve>closed</valve>  </tyre>
<tyre>      <valve>open</valve>  </tyre>
<tyre> air, <valve>closed</valve>  </tyre>
</car>

Maybe I just like the idea of a closing tag being very specific about what it is that is being closed (?). I guess I'm really not sure, but it does feel nicer to my brain to have starting and closing tags and distinguishing between what is structure, what is data, what is inside where.

My peeve with json is that... it doesn't properly distinguish between strings that happen to be a number and "numbers" resulting in:

myinput = {"1":"Hello",1:"Hello"}
tempjson = json.dumps(myinput)
output = json.loads(tempjson)
print(output)
>>>{'1': 'Hello'}

in python.

I actually don't like the attributes in xml, I think it would be better if it was mandatory that they were also just more tagged elements inside the others, and that the "validity" of a piece of xml being a certain object would depend entirely on parsing correctly or not.

I particularly hate the idea of attributes in svg, and even more particularly the way they defined paths.

https://developer.mozilla.org/en-US/docs/Web/SVG/Tutorial/Paths#curve_commands

It works, but I consider that truly ugly. And also I don't understand because it would have been trivial to do something like this:

<path><element>data</element><element>data</element></path>