I can point to a decision that the agency had before it shortly after Air Canada decided to discontinue its pets-in-cabin program. We had a complaint from someone who wanted to travel with their pet and found this new change in policy was unreasonable.
The reason that Air Canada gave to the agency for that change was they had complaints from persons with allergies. They also had complaints from other travellers just about the nuisance factor of having dogs in the cabin. So it was largely feedback that they had received from their travellers, and that was their decision.
I think you'd be best to ask Air Canada why they have changed it again.