I don't really think you would have 80,000 willing prisoners, but even if they did have them, do you think it would have been possible to sacrifice 20,000 people a day? That comes out to 833 people per hour if the priests worked 24/7, and how long does it take to kill a person in a sacrifice? I would think they would have at least some ritual for each kill. Better said I believe this is a lie, just made so Europeans would believe the same lie that has been perpetuated, that they in reality came here to enlighten the natives.