Why? MFA via SMS is the most user friendly option at this point. Nothing else comes close.

The Apple flow... - Visit site/app - Clock "send code to phone" - Apple populates code field with code when it arrives

No 3rd party app, no extra subscription, no extra hardware. Couldn't be much easier.

Yes, I realize SMS can be attacked in a few ways that app- or hardware-based MFA cannot. But, it's probably better than nothing (I've not seen a good counter to it).

Now, should banks offer SMS + app/hardware options? Absolutely. No question. But please don't take away SMS unless you're offering something just as easy.