One's a dictionary (unordered, simple unique keys), and one's a list (ordered, arbitrary contents, no uniqueness constraints). Schemas may enforce more, but those are the intrinsic qualities.

I agree that use varies widely, but the difference is fairly clear. The existence of nonsense doesn't mean one can't make good decisions.

Is it more logical to have a point tag which has the attributes x and y or have x and y as their own tags and values? Its not clear to me which makes more sense and it seems the spec writes using xml didn't know either.

since x and y are simple names, have simple values, and are unique pairs that apply only once to a point: attributes.

to use anything else means relying on an arbitrarily-complex custom schema rather than the much-simpler-and-far-more-standard schema of the language itself. similar to how we use datatypes in programming languages rather than just strings everywhere. both work! one is clearly giving up a lot, and gaining little.