> Every single one of them oversells their capacity

This is (almost) universally true of flat rate subscriptions; but there are usage-billed ones, too (and even those often have an aspect of subsidies).

A great example of the shakeup is when dial-up went from "connect, do the thing, disconnect" to "leave the computer online all the time" - they had to change the billing model because it wasn't built for continuous connections.