In a small unventilated closed room you'd be right - the aerosol from mask leakage would saturate the room and the masks would be useless. The kind of masks tha

In a small unventilated closed room you'd be right - the aerosol from mask leakage would saturate the room and the masks would be useless. The kind of masks that most people wear are mainly useful for preventing direct droplet transmission when two people's faces are in close proximity - especially when there's talking involved. However an airliner is extremely well ventilated - the entire cabin air is refreshed every 3 minutes, through a combination of HEPA filters and fresh outside air. In addition, the airflow in the cabin is vertical - new air is introduced at the top through the nozzles you're used to, and the intakes are by your feet. This means the risk from ambient aerosol transmission is much reduced and direct droplet infection becomes the primary risk vector. I would absolutely expect to see a reduction in transmission if everyone kept wearing masks.