An app pin isn’t going to help if someone is using threat of violence to get into your bank apps. The only thing that would really help in this scenario is a pre-emptive choice to limit the number of finance apps you install on your phone (i.e. don’t install the ones with access to very large sums of money). But that doesn’t mean an app pin wouldn’t be helpful for other scenarios.
I don’t know about the “like almost everyone else” bit. Monzo is the only finance app I have that falls back to device passcode as an unlock method. The others must have had in mind that having an layer of protection beyond device passcode is desirable.