This is a fundamental problem of value creation and value extraction. Just because the ISP's can't extract the value of adding the additional fiber capacity doesn't mean it doesn't confer that value to the customers. We live in an age of value extraction, what's colloquially known as "enshittification", that can't go on forever. Somebody has to create the value that is being extracted.

It's the old Marx quote: "From each according to his ability, to each according to his need". Except you know, the opposite.