|Don't ask to ask, just ask
I think I understand what you're going through. I've also been at clients that for one reason or another decided it would be better to re-invent the wheel, then did a poor job at it. It's not just Perl, either. I've seen it with many other languages and technologies. There seem to be a few common reasons (excuses) I run into:
Each of these has a reasonable response, but you need to phrase it such that someone with a business perspective will understand you. Probably the strongest argument would be to remind them that CPAN can affect budgets and delivery schedules very positively!
It appears you've grown disenchanted enough to want to throw in the towel. I don't know your circumstances, so maybe that is the right thing to do. But if it's just a question of "better late than never", I encourage you to go ahead and try to make your case. If you need specific arguments, post again. Many of our senior monks are both articulate and wise, and would probably be only too glad to help.
In any case, hang in there.