That would make sense if ISPs' costs veried per GB like a power suppliers costs vary per kWh. But they don't really. 99% of the cost of them is running the init

That would make sense if ISPs' costs veried per GB like a power suppliers costs vary per kWh. But they don't really. 99% of the cost of them is running the initial fibre/copper and then maintaining it. Until you reach the limit of the infrastructure, the cost per extra GB is basucally nothing.