But most people aren't streaming 24 hours a day, but only in a specific period. So if the plan is 300 GB/month, then having higher speeds is more interesting than having slower speeds (especially if a slower speed doesn't let you actually use all your data)
That's sort of where it went wrong. You offer video streaming rates and now people think, cool, tv, let's turn it on all day.
If you offer data rates where you can afford to offer fair use, then each year you can offer higher data rates. Which is what people like.
Where I live, I see this problem mostly on mobile. You see telcos offer insanely high 4G data rates and a data limit that is low enough that you can burn through that in a couple of minutes.
The net result is that nobody cares anymore. In general, people don't want to keep track of their uses. It makes for a poor experience.
So they can easily get back to fair use by limiting speeds to a couple of megabits. Of course that would kill streaming tv.
Another way of looking at it, you can listen to audio 24x7 and not go over quota. Watching tv all day every day is not going to work.