Every banking phone app I've used auto-logouts after being idle or unused for a bit, and my primary bank's app requires 2fa using an app that exists on the same device -- a second factor that secures nothing. They probably are not explicitly considering the phone more secure than a computer, but rather a good 80% of this is security theater or a checkbox on some baseline security checklist that was implemented without really understanding what the implications, for usability and security, were going to be.