I wouldn't put it past this bunch of cowboys to simply dream up various charges off the top of their head. Besides the real answer is probably the dopes that are Air Canada's software engineers did only half a job and are charging outbound pax only.

With AC the charges are simply inventions.
For instance to redeem Continental miles and go from Dallas to Calgary on One Pass points will cost you the 25000 points and 56 dollars in fees. Now to go on Air Canada it will cost you 25000 points and 96 dollars in fees. Then the website won't let you book it and so you need to tack on another 30 bucks booking fee because their POS website is a joke.