"Are all these modules written in other languages because they really cannot be done in perl alone?"
The good thing about Perl is TIMTOWTDI, and the same goes for CPAN. If you want a pure perl way to handle CSV files, go for Text::CSV_PP, if you don't care about it being pure perl and you'd fancy speed (like me), you'd go for Text::CSV_XS.
I don't see the problem here. Perl isn't great at everything. I'm not writing up a Perl program when find + xargs can do it better/easier. I'm not building something myself something when bzgrep will be faster/easier. (Although I do use ack more often than grep nowadays).
Perl isn't always the right choice. Often, yes, but sometimes other languages come in handy too. In the above CSV example, the XS part will most likely speed it up. I'm really curious how you'd think something like Net::SSLeay or ImageMagick would be created without compiling evil non-Perl code, though. And what modules using non-Perl code modules trouble you this much if I may ask?