They do not.
The format where they do is when it is a service provider and they simply stop service of the contract. I.e. if you don't accept the terms and services for say, using reddit, they can just choose to not continue providing you access to those servers.
But it didn't hold up on contracts involving already rendered services or anything really other then the outcome of declining being 'everyone exiting the contract' or simply moving back to the previous contract.
Courts in the us have pretty much universally upheld that contracts cannot be changed without all parties agreeing.