XML was a product of its time, when after almost 20 years of CPUs rapidly getting quicker, we contemplated that the size of data wouldn't matter, and data types won't matter (hence XML doesn't have them, but after that JSON got them back) -- we expected languages with weak type systems to dominate forever, and that we would be working and thinking levels above all this, abstractly, and so on.

I remember XML proponents back then argued that it allows semantics -- although, it was never clear how a non-human would understand it and process.

The funny thing about namespaces is that the prefix, by the XML docs, should be meaningless -- instead you should look at the URL of the namespace. It's like if we read a doc with snake:front-left-paw, and ask how come does a snake have paws? -- Because it's actually a bear -- see the definition of snake in the URL! It feels like mathematical concepts -- coordinate spaces, numeric spaces with different number 1 and base space vectors -- applied to HTML. It may be useful in rare cases. But few can wrap their heads around it, and right from the start, most tools worked only with exactly named prefixes, and everyone had to follow this way.