> They do not actually exist in the language to be parsed (unless that language is not well-specified

How do you specify your language “well” when you don’t know if your grammar is unambiguous? Determining whether a grammar is ambiguous is famously undecidable in the general case. So how do you decide, if you don’t restrict your grammar to one of the decidable forms checkable by parser generators? You can add some disambiguation rules, but how do you know they cover all ambiguities?

We use formal systems exactly to make sure that the language is well-defined.