Poor ISPs can't deliver the broadband that we pay for and now it is the customers fault. :(
Just like the electricity utility companies cannot provide everyone at the same time with the maximum power they are allowed to use.
We also know from poorer countries that ISPs can provide better connections.
With an electricity utility, they may be able to turn on their coal generators to meet peak loads - it's a higher cost, but it's something they have available to use when needed. If engineered correctly, it also provides power consistently across all customers. Sure your house never uses enough to matter, but if all of a sudden an auto manufacturer wanted to turn on a whole new production line, they would have planned for that and gotten specific lines run to power it.
There is no equivalent for an ISP. Yes, they could guarantee that each customer gets x mbit/s and provision enough capacity (both to your house, to your neighborhood, to your central office, and finally to their peering connections) to cover all of that, but your internet would cost $300/m whether you use it or not and you'd be complaining about that too.
In the US? The fact that everybody doesn't hate their guts. A future government could easily screw them over in the future, because the voters don't like those companies.
In other countries? Competition. You offer a better service than other ISPs. This also gives everyone better internet and internet services can offer more things. Much poorer countries than the US and Germany have much better internet for a lower cost. As long as there's a big disparity there customers aren't going to be happy.
Each measure could be based off of what the ISP has factored in for the "average" usage at a given time. It would be a purely synthetic number, but it would give people a better idea of exactly what they use, when, and how that compares.
You’d have to ask your neighbor about their usage to get comparative metrics, tho.
Apparently in March 2019 I used a total of 106GB of download 25GB of upload, and this month so far is way below those numbers. This is biased by me working from home, so hour-long video conference calls aren't a new thing for me.
The ISP's policy (for which they charge significantly more than a typical ISP in my country) is to "never be the bottleneck". If things are too slow it is never (intentionally) their fault. So that's one reason they provide these charts - you can see latency info in them, drop rates, everything.