Aisle-to-window wouldn't work because you'd get lots of the aisle people now clogging the airplane exit passage as they wait for their friends and family to com

Aisle-to-window wouldn't work because you'd get lots of the aisle people now clogging the airplane exit passage as they wait for their friends and family to come out. People traveling as a group sit next to each other. Exiting by column absolutely guarantees that people in the same group will exit at different times, which means they have to wait for the entire airplane to deplane anyway in order to put their group back together. Exiting by column really only helps solo travelers.