Comment by wyager

Because people implement parsers in languages that don’t allow direct expression of grammars (e.g. C). To safely implement parsers you must choose either algebraic datatypes or continuation passing, and a lot of programmers choose neither. CPS is annoying in most languages. ADTs are the obvious choice but somehow in 2021 most people are using languages that don’t have them. If you write a parser in Haskell, for example, you’d have to mess up pretty badly and write totally non-idiomatic code to write a parser that crashes at all, let alone crashes in a way that compromises memory safety.