I don't doubt that there are existing libraries and modules that allow one to create some parser. The question is always "how suitable are those libraries for my needs?". After struggling through documentation for few libraries just to find out that they don't completely fit, I came to conclusion that it is simpler to create my own parser. So if you like it, in my post I was trying to say that creating a parser is not very hard and in certain cases it makes no sense to waste your time on understanding how some existing parsers work, it is better to use it for creating the parser that perfectly suits your needs.
I hope this clarifies your confusion :)