Then why isn't that happening on Android with Google Pay? Banks are able to handle NFC payments through their own apps if they want, but the vast majority support Google Pay and don't force users into their own app.
I suspect that is largely due to the success of Apple Pay. Banks used to have their own apps on Android for years and only grudgingly started to support Apple Pay since they couldn't use their own apps. They only started migrating from their own apps to Google Wallet/Pay after Apple Pay became a success and Android users started to feel left out. They would never have supported Apple Pay if they hadn't been forced to do so. In fact, even though there was no alternative they kept dragging their feet and complaining about it for years.
Why would you use apple pay if you are planning to use a banking app? Isnt the point of having a banking app so you dont have to completely depend on apple pay?
Maybe the ui app will stop being shitty as the usage goes up? That is the point