I'd argue that banks DO need to know that you've unlocked your bootloader, but they should present you with a "Your phone bootloader is unlocked. If you don't know what it means or you didn't do it yourself, exit the app now and contact customer support."
The problem is that app makers are lazy.
Ehhh most peoples' bank accounts don't get compromised by someone getting a hold of their phone long enough to hack their bootloader.
Not to mention Android deletes all your apps and cache if you go from locked to unlocked, and you have to reinstall all of them again.
So if I call in on the phone do they need a video feed of my surroundings to verify that I'm not being extorted? Perhaps if I come into a branch in person to make a large withdrawal they need a drug test to ensure that I'm not intoxicated?
They absolutely do not have any need to know anything about my bootloader or OS version or safety net or otherwise. It's certainly true that it is within the realm of physical possibility for them to put that information to good use in a responsible manner if they had access to it. But being able to make use of something is not the same as a legitimate need.