Are they not cheaper to operate because of economies of scale for staff (fewer sailors per ton-mile of cargo) and fuel (one big hull is less drag through the wa

Are they not cheaper to operate because of economies of scale for staff (fewer sailors per ton-mile of cargo) and fuel (one big hull is less drag through the water than tons of little ones)? I assumed those were the main reasons but maybe there is some bigger one that dwarfs these, perhaps construction costs? Docking fees?