For each module on CPAN (as returned by the cpan shell command m /./), cpan -r searches the directories named in @INC for a DLL named after the module (e.g. auto/Foo/Bar.so or auto/Foo/Bar.dll for module Foo::Bar, depending on your system). If the DLL is found, it flags the module for reinstallation.

You claim you never installed any modules, but some were installed along with Perl, and some of those are dual-lived. cpan is reinstalling those (e.g. Storable).

There are no sources on your machine, so reinstalling requires downloading.

It downloads the latest version of each module. This may introduce new dependencies.

By the way, you appear to be saying that "Unsatisfied dependencies detected during" is an error, but it's not. It's just a list of modules the distribution is requesting to install.