On a higher level, the fact that so much different kind of information could exist at each level was nothing but headaches. In YAML, or in JSON, it's pretty straight forward. You have an object, it has children, children have types/values etc.
In XML, you have to keep in mind what the tag of the element, what its attributes are, and then what the child elements are, and then whatever the heck CDATA is.
I think my fellow posters are looking at the past through nostalgic rose tinted glasses. XML was terrible and I am glad it's not used as widely anymore.