XML lost because 1) the existence of attributes means a document cannot be automatically mapped to a basic language data structure like an array of strings, and 2) namespaces are an unmitigated hell to work with. Even just declaring a default namespace and doing nothing else immediately makes your day 10x harder.

These items make XML deeply tedious and annoying to ingest and manipulate. Plus, some major XML libraries, like lxml in Python, are extremely unintuitive in their implementation of DOM structures and manipulation. If ingesting and manipulating your markup language feels like an endless trudge through a fiery wasteland then don't be surprised when a simpler, more ergonomic alternative wins, even if its feature set is strictly inferior. And that's exactly what happened.

I say this having spent the last 10 years struggling with lxml specifically, and my entire 25 year career dealing with XML in some shape or form. I still routinely throw up my hands in frustration when having to use Python tooling to do what feels like what should be even the most basic XML task.

Though xpath is nice.