And this almost certainly means that the bank took a fraud-related monetary loss, because the regulatory framework that governs banks makes it difficult for them to refuse to return their customer's money on the grounds that it was actually your piano teacher's fault for being stupid with her bank app on her smartphone (also, even if it were legal to do so, doing this regularly would create a lot of bad press for the bank). And they're unlikely to recover the losses from the actual scammers.

Fraud losses are something that banks track internally and attempt to minimize when possible and when it doesn't trade-off against other goals they have, such as maintaining regulatory compliance or costing more money than the fraud does. This means that banks - really, any regulated financial institution at all that has a smartphone app - have a financial incentive to encourage Apple and Google to build functionality into their mass-market smartphone OSs that locks them down and makes it harder for attackers to scam ordinary, unsophisticated customers in this way. They have zero incentive to lobby to make smartphone platforms more open. And there's a lot more technically-unsophisticated users like your piano teacher than there are free-software-enthusiasts who care about their smartphone OS provider not locking down the OS.

I think this is a bad thing, but then I'm personally a free-software-enthusiast, not a technically-unsophisticated smartphone user.