As others pointed out, every business that sells capacity does this, including your ISP provider.

They could, of course, price your 10GB plan under the assumption that you would max out your connection 24 hours a day.

I fail to see how this would be advantageous to the vast majority of the customers.

Well, if the service price were in any way tied to the cost of transmitting bytes, then even the 24hr scenarios would likely see a reduction in cost to customers. Instead we have overage fees and data caps to help with "network congestion", which tells us all how little they think of their customers.