For the same reason an organization will ask you to fill in a standard form page (even on paper) rather than writing a long form essay.

Why do they do that, again? I'm not arguing against summaries. Just saying that if machines can read as well or better than humans, then machine-readable in the sense of using a simplified ontology, grammar, or alphabet is unnecessary.

My point is that even humans make fewer mistakes when they're reading an established form structure with pre-defined fields over long-form text. Hence you'd expect a machine to process them better as well, even if it could read like a human.

Because even if you can read you need context, or you need to be able to identify what a new word means. Reusing a shared vocabulary is useful.

I don't understand. If you already agree on a shared vocabulary, then you're not using new words. Context is more present in the long-form un-pre-processed text than in the short-form text.