Attributes have datatypes. Attributes take less space since they have no start and end tag. Values containing quotes can be a bother. Attributes can't contain other elements. White spaces can't be ignored in attributes.
Attribute values are harder to search for in search engines.
Attribute values often don't appear on the screen in editing tools. Attributes can be slightly more awkward to access in processing API's. Attributes are unordered. Example 1 - Books 1. The only important thing is that the object is a book.