Banks have the advantage that if they see a huge spike in their outbound inter-bank transfers they can suspend traffic while they investigate it, and then if ne

Banks have the advantage that if they see a huge spike in their outbound inter-bank transfers they can suspend traffic while they investigate it, and then if necessary call up the recieving bank(s) and issue a freeze on those funds. There's already established relationships and agreements for these things. With a cryptocurrency there's nobody to call, you have to convince 50% + 1 of the mining pool to undo any major breach - which is almost certainly never going to happen.