But I am a bit at a loss to understand why they don't release inventory on low-demand flights.
You could ask UA exactly the same question. If anything, UA is a far worse offender in terms of not releasing saver space to *A partners, including AC in particular.
The answer is that carriers want to lock their customers into their own frequent flyer ecosystem, rather than encouraging them to spend money acquiring different loyalty program currencies. Once you recognize that frequent flyer programs are intended to benefit the sponsoring airline, and
not the frequent flyer program members, it will all make much more sense.
BTW, I just purchased some Aeroplan miles with 85% bonus and completed my transaction on the AC side. .
Bingo.
Correct, thought the price could be highly variable. I have seen those vary by as much as a factor of 4 on the same route and class of service.
You mean like UA's dynamically priced YN and JN awards?