It's about the policy creating the trend of apps that don't work in that you can't sign up on them.
You get the first, then sign up on the website or android app.
Try again.
Update: I just double checked. The Wells Fargo Android app and Wells Fargo iOS apps behave identically. You are immediately presented with a login screen upon launch. There is no signup flow inside either app but you can click a link that opens a web browser with a link to the registration page.
Your claim that the App Store policy is responsible for this trend does not hold up, considering the Android version is not subject to the same policy but behaves the exact same way anyway.
Update 2: Checked a few more apps. The Android versions of Github and Fastmail don't allow you to sign up in the app either. You are only presented with a login screen just like the iOS versions.
Don't remember if they had a link for signups before though, just pointing out that you can't deduce that point from given facts.
(Nor is there proof for the original thesis, it's all speculation at this point)
To circle back to the original point, blaming Apple for the "trend" of not being able to sign up inside of apps is clearly nonsensical.
This whole website is a strawman built against the false claim that you're not allowed to require a login to access your app, which has never actually been true.