Any backdoor made for law enforcement will eventually land in the hands of bad actors, and sometimes those backdoors will be used illegally by law enforcement.
It's a practical feature in general, to allow anyone to poke through your phone without installing/posting/reconfiguring anything, occasionally nice to have. Then again, it would also slightly increase the social normalcy of being able to ask to snoop through other people's phones.
So they can use the banking app to transfer money away from your account because that's not stored locally on your phone? Or to look at your private photos?