One thing is sure, every customer an ISP gains, is more profit in their pockets, regardless if the customer downloads 200GB per month, or only 1GB.
Even if ALL of their customers would download 100GB per month they would still be able to run fine with their $50 per month plans.
Construction costs, maintenance is very negligable. Every 7 years they will need to renew their servers, but who the heck said they needed to go for that ultra fast $100.000 server, if 2x $30.000 servers could outpace the 100.000 one?
Get 2x 30.000$ servers instead, and wait 3 years, and then buy that 100.000 server additionaly (or a better one) for the remaining $40.000 or so...
But some ISP's have donkey dicks in their offices, wasting money like leaving AC's running with all doors and windows opened!
Get real! The customer don't need to pay for the company's inadequency to handle the money!