The DAO incident was a special case. It was only sane to do the rollback because the stolen funds were time-locked up for 28 days.

Ethereum never did it again, rolling back hacks didn’t (and couldn’t) become normal policy. IMO, they shouldn’t have made an exception, as it set a bad example.

I’ve seen a few other small projects attempt to do rollbacks since, but it usually turns into some kind of mess. In most hacks, the coins aren’t time-locked and quickly get laundered through smaller exchanges (and other services) which act as mixers. The stolen coins end up in the hands of a bunch of innocent people, and the rollback then causes way more harm as those users lose their coins.