Aeroplan is just yet another of these crooked operations that make something out of nothing, and with zero value for society as a whole.
For AC, however, it is probably their No. 1 customer. AC no longer has seats with zero marginsl value that it could use as essentially free stuff to allocate to rewards.
Instead, Aeroplan has turned into a way for AC to sell these seats ahead of time at a contracted price. Which may not be high, but is high enough that nowadays they price it so that FF awards come across as expensive.
Bottom line, AC now has to account for FF benefits in ways that make these compete with Aeroplan.
The crooks win, honest people such as you and I lose. Welcome to the 21st century.