Full =/= revenue sales, could be from upgrades or staff standbys.

I'm sure AC had the financial data to make that decision and also looking at the bigger picture into Rouge's model. Perhaps it's more profitable/reliable to sell ACV packages with 12 extra economy class seat than 4 people willing to pay business class fare. Not to mention there's still a 8 net increase in headcount, that's 2-4 more ACV packages/hotel rooms sold.

Also people are likely be willing to downgrade than otherwise being priced out of a trip because the only seats available is in business class or the flight being completely full.

While I think getting there is (more than) half the fun, most people flying on Rouge to sun destinations see the flight as merely a mean of transportation and usually put price over comfort.