The league pays several million a year as contribution towards the Northern Stand (the Southern stand already paid off), but my understanding is that this doesnt include match costs which are paid by the host club. Last year the MCC reports AFL revenue was 7.4m - and they barely played a game. The year before that AFL revenue was 9.5m and they played a whole season, finals and the grand final.
That clarifies my understanding of why the clubs were not charged rent for 2020.