> why am I paying for bandwidth on AWS? Shouldn't that be paid for by the downloading party?

you're paying for it because it costs money to provide bandwidth on both ends, and AWS is just shunting the cost onto you itemized.

Netflix, believe it or not, also charges for the bandwidth it uses, but it hides it unitemized into the subscription fee, and in sufficient quantities that when averaged across all it's subscribers, they come out at least breakeven.