I was thinking the exact same thing. I'm not going to say that there are no valid reasons or situations where modules aren't allowed, but it's very hard to think of one that doesn't involve, "because I'm supposed to write this functionality myself as homework".

worst-case scenario, you can almost always bundle the modules into your own application, or utilize modern tools like App::FatPacker to do the work for you.

Programming in Perl without CPAN is like going into a gun fight without bullets.