Because it is a secure environment and I may not use any non core modules, other than those I write...
Who came up with that nonsense idea? What makes core modules so special that they are suitable for a "secure" environment, but other modules from CPAN aren't? And what about that "insecure" CPAN modules that become core modules during the development of Perl? How do they suddenly become "secure"? Is the entire Perl source code subject to a code review?
Or is "security" once more a lame excuse not to use CPAN? See also Re^4: CSV file with double quotes and NIH syndrome.
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)