You can roll back Ethereum transactions without forking the blockchain if you build the rollback mechanism into your settlement contract.

There isn’t anything to “fork” in USD since it isn’t a blockchain, but different USD settlement layers get out of sync and have to be manually reconciled. If you instead tried to “fork”/replicate USD in that situation, you’d probably be thrown in jail for life. I personally prefer the blockchain way of expressing my option through code and seeing if anyone wants to follow me and not having to ask for permission.