What many people don't realize is that this is a form of what's called 'CPP integration'. That is, your retirement benefits are reduced by the amount of your monthly CPP cheque. So instead of getting your CFSA payment in full, with your CPP cheque on top of that, you get a portion of your CFSA cheque topped up by CPP. I'm currently a federal civil servant, and when I retire at 60, but start collecting CPP at age 65, the same thing will happen to me.
It's really just a way to make your pension last longer and keep the CFSA/CPP pension plans solvent. It's all money coming out of the same pot of general government revenues, anyway.