ISPs pay a more or less fixed rate for their infrastructure regardless of how much it's used, and it's inherently rate limited. You can't make a 1 gig connection go faster than 1 gig or use more power than it would at 100%. The reality is though that customers rarely push it to 100% so actually they save a ton of money making people share bandwidth.
I don't understand your analogy, but what I said is not silly.
Internet service providers sell you access to the internet. They don't own/create the data on the internet, they provide you with a connection. Just look at the packages they sell. It's bandwidth. (Except in some markets they have data caps but that's bullshit rent seeking)