Because as per usual they don’t understand security. I have started choosing my bank based on software they have. If software looks competent, that’s my most significant influence.
They think rooted device = insecure device, but at the same time PC is even less secure and yet all the business users use them and more to the point have passwords written on a sticky note glued to the screen. My old bank at one point “upgraded” their software system and then started asking me for weird characters in password and then asked for maximum length which was the final sin I allowed them to commit. Left them that week.