XML "lost" because it is also a poor format for structured data. It requires constant choice between whether some content should be conveyed using attributes or child nodes. If you use child nodes, indentation may or may not be relevant (because it can introduce leading/trailing spaces). There is also no standard for data types. (Do you write a boolean attribute foo as foo="foo", foo="true", or foo="yes"? Sure, a schema can describe the allowed values, but whoever interprets the XML still needs to add the right translation to true and false in their programming language by hand, presumably.) Due to the manifold ways of expressing essentially the same data, working with XML is always painful.

This is not really XML's fault. It was designed as a way of marking up text. When that is your goal, XML is not a bad choice, and all of its features make a lot more sense. (For example, this child-attribute distinction: Is this part of the text? If so, it should be represented as child nodes. Otherwise, it should be an attribute.) Here, something like JSON really falls flat.

But most data is not marked up text. And yet, some people and institutions tried to push XML as the universal solution to all data transfer problems. This is the reason for the push-back against it.

This isn't to say that we did not also lose some things. In complex cases, having something like a schema is good. Comments are appreciated when the files are also read and edited by humans. JSON's data types are underspecified. But I firmly believe that the solution to this is not XML.