False. A month is a discrete amount of time that yields a potential maximum amount of data downloaded, this amount is clearly related to the bandwidth provided, hence caps.

To think otherwise is to falsely believe they support unlimited throughput. Furthermore the bandwidth itself literally is a function of the transmission material and infrastructure, which also isn’t free…

I have a 500 Mbps connection with a 1TB data cap, both pretty standard numbers in the US. If I used the connection at its advertised speeds, I would exhaust my monthly limit in about 4 hours. So no, that relationship is non-existent. The data cap math instead is "99% of our users use < 1TB, so we will charge the rest more because we can".

Or more accurately, to disincentive excessive use. They don’t need a cap to simply charge you more money, they’ve been doing that just fine with or without caps.

If that was a big issue, why are smaller ISPs (like sonic.com) able to offer 10Gb ethernet at a flat rate with no caps?

That would be a valid argument if they defined "excessive" based on infrastructure limits rather than a demand curve and market research.

All prices are based on “demand curve and market research” so I’m not sure what your point is.

My point from the start has been that ISPs put data caps and overage charges in place to make extra money, not to protect their infrastructure.