why not?
Because numpties respond to phone calls from fake bank fraud departments all the time and told to send their money to other accounts for 'safekeeping,'
Similarly you get man in the middle stuff where the bank details of house sales are sent through a hijacked email and off goes someone's money to a scammer.
You'd think that since it's all on their ledger banks would be able to squash moves like this flat immediately but a lot of the time they don't and tell the customer they're on their own. Crypto totally removes that ability, not that they seem to exercise it at present.
This is how it is in the UK where bank transfers are instant and free. It may well be different in countries with third world banking like the US.
it would actually work quite the same. if banks already tell customers they're on their own with bank transfers, why can't that apply to crypto? crypto doesn't remove that ability at all since it's all internal ledgers until interbank settlement occurs. whether we're talking bank wires or on-chain settlements between banks, once interbank settlement occurs, customers who got scammed are out of luck because the money is gone. same as today.
banks may protect consumers from fraudulent use of credit cards under specific circumstances, but it's not their job to reimburse customers for irreversible payments like wires and cash withdrawals. the same applies to crypto depositors who withdrawal to external addresses.
within the banking app, i think it would work the same as credit cards today---you have a trusted network processor like mastercard. these can be protected from fraudulent use like credit card purchases because it's pre-settlement.