I expect to see this soon as a way of combatting people who join one for a month or two, binge, then switch to another provider.
It might not come in the form of contracts at first, maybe they will just jack up the price of month to month high enough that people will voluntarily buy into a contract or yearly pre-purchase.
Trust me, there is always a way to make more money if you’re OK with being anti-consumer. It’s just a matter of time.