I agree that many of the modules I install using cpanm take a long time, where long can be tens of minutes. There are reasons:

• Many modules have a compiled C component which is compiled on the local machine.
• Almost all modules depend on other modules - that's kinda the point of having a module library in the first place. If the dependencies aren't already installed they need to be fetched and installed - rinse and repeat.
• Good modules come with comprehensive test suites that are run on your machine to check that there isn't some unforeseen incompatibility or bug due to your environment.

My limited understanding of Python module installs is that they amount to copying a file. From what I've seen there is no install time dependency checking. I may be misremembering on both assertions, but if not the work that is done for a Perl module install is very different than Python. In principle that means that a Perl module that installs correctly should have everything it needs to actually work correctly on your machine. My very limited experience with Python is that is not generally the case.