You can't just generalize all PoS as being the same code and execution. ETH is quite different from the rest. Furthermore, none of the other blockchains have even close to the level of value (not just $ amount, but also fame) tied up in them.

As for rollback... that's what created ETC, but this time, it is different... with PoS, the 'stake' is tied up in the network. It isn't external, like it is with PoW and isn't as easy to just fork. You're effectively now forced to convince everyone to follow another canonical chain, but you don't have an external way to do so. Forking becomes a lot harder. It also becomes a lot more complicated and hasn't even been done before... how much 'testing' has that gotten?

How are exchanges going to agree to rollback after they have already exchanged those tokens with others? Someone has to burden the loss, so it might as well be the original blockchain that got exploited.

Yes! This is exactly the premise of Jeff's essay [1] that I mentioned in comments below.

This gets messy fast when there is an issue and even worse is that there isn't a published plan for how to deal with things when they do come up. Everyone is betting on it all executing perfectly and given the complexity and value at stake here, chances are that at some point now, or in the future, it won't go well.

[1] https://github.com/stickfigure/blog/wiki/Proof-Of-Stake-Wear...