Because processing actual applications in order for a PPR to be issued has nothing to do with you sending in your passport.
If they delay working on the applications for the length of time that CP is on strike, they're going to be left with a backlog that'll cost them.
They can process an application - if you are denied then that's the end of that story. A Canada Post strike will have no immediate or future impact on your application. If you are denied, Canada Post is the least of your worries.
If you are approved, then there is still a step BEFORE you are issued a COPR. Again, this step does not involve Canada Post. Canada Post plays no role in whether you do, or do not, pay your fees.
It only plays a role once your passport comes into play. And we're all a few steps behind THAT.