This is one of the problems, and it might be the biggest problem with the modern web, but it's not the only problem. Non-experts are bad at producing remixable content.

* A significant number of people do not really use file names. https://jayfax.neocities.org/mediocrity/gnome-has-no-thumbna...

* Twitter offers no official way to make bold or italic text, but some people make it work using math symbols. They either don't know, or don't care, about all the accessibility and search tooling this breaks.

* Try downloading a C program off the internet and compiling it on anything other than the original developer's computer.

In none of these cases does anybody benefit from the lack of usable metadata, yet nonetheless the metadata doesn't exist.