They largely have moved this way. Most their plans now throttle the bandwidth when the cap is exceeded instead of charging for overages... so you can keep internet'ing away but at slower speeds and without surprise charges. And their data caps are pretty generous; I'm paying for a 100 mbps connection with 250 GB cap per month -- no way do I ever approach 250 GB per month, even with a lot of Netflix streaming.

Unlimited bandwidth is a bad idea and that's why those plans have largely gone away -- it invites abuse. 1-2% of the users end up using 90-95% of the bandwidth and slowing things down for everybody.