> some apps don't support text selection and on some websites the text selection is unpredictable.

That correctly identifies the problem. Now why is that, and how can we fix it?

It seems fixable; native GUI apps have COM bindings that can fairly reliably produce the text present in certain controls in the vast majority of cases. Web apps (and "desktop" apps that are actually web apps) have accessibility attributes and at least nominally the notion of separating document data from presentation. Now why do so few applications support text extraction via those channels? If the answer is "it's hard/easier not to", how can we make the right way easier than the wrong way?