in the same way that a Utility Company probably isn't gathering enough water for everyone to be maxing their pipes 24/7, residential ISP's don't operate under the assumption that every consumer will have maxed their connection at the same time
That's not what's happening, though. What's happening is that the ISPs have not provisioned enough capacity to serve the actual aggregate demand at peak times. The hydraulic analogy would be if water pressure dropped every day between 0800 and 0900 because everyone was having their morning shower. That would not be acceptable to customers, and nor is the situation with ISPs.
What's more, the utility company is getting water through a pipe that goes to a middleman near a river, but that pipe doesn't have enough capacity to deliver the water necessary for all utility customers to take their morning shower at the same time. So what does the utility company do? It blames the middleman and the river for "sending too much water"... and demands payment from them!!!
As I see the graph in the post it looks like the customers have full pressure only between 3 and 4AM. In the rest part of the day they are struggling to get their shower.
That's not what's happening, though. What's happening is that the ISPs have not provisioned enough capacity to serve the actual aggregate demand at peak times. The hydraulic analogy would be if water pressure dropped every day between 0800 and 0900 because everyone was having their morning shower. That would not be acceptable to customers, and nor is the situation with ISPs.