Why don't the book include the Interpreter pattern?

The Interpreter is probably the least used and most complicated of all the GoF patterns. That was the reason why I didn't bother to include it in the book. Here's the link I like to present when people ask me about the absence of the Interpreter in the book: http://blogs.perl.org/users/jeffrey_kegler/2013/03/the-interpreter-design-pattern.html