I have long thought that ISPs should charge by bandwidth used. It would incentivize improving infrastructure. Any ISP that would charge by bandwidth used would want their customers reselling bandwidth.
No it wouldn't. The actual usage has a negligible impact on the expenses for infrastructure. Most people barely use any bandwidth anyway. Even on 1 Gbit/s lines the average bandwidth used is in the single digit Mbit/s. And the usage basically doesn't differ if they have a 100Mbit/s or 10Gbit/s connection. Also those countries where data caps are still a thing are generally those with the worst Internet.
Netflix and YouTube show us that many people want more bandwidth.
There would be no data caps if paying for bandwidth consumed.
Both don't require a lot of bandwidth and you have caches for their content.
You can buy additional data if you've used your included data. That's basically the same.
How?
That doesn't seem to work in any industry that is close to being a utility. Just look at toll roads.
If you live in a place with only one or two ISPs and they only charge a flat rate per month for capped usage, you never get more bandwidth. The system is working as designed.