This is a relatively straight forward request that maybe doesn't go as far as most people imagine here. Pressing "delete" doesn't instantly delete all user data and it's not expected to. In some cases there may be subsequent steps and some data may be kept for legal reasons*.
The point is very sensible, if I can request the creation of an account or subscription easily in the app, the reverse process should be just as straight forward. If an app can give a one button "create-subscribe-pay" experience then when it comes to deletion you shouldn't suddenly fill out paper forms, or send letters at specific times in the month. And that's if you can even find the info on how to do it in the first place.
Now you can trigger the deletion and know that they have to do something about it, at the very least get clear instructions on how to proceed.
*When it comes to banks, they are subject to laws and regulation that many other companies/services don't have to deal with. Which is why Apples makes this provision:
> We encourage you to review any laws that may require you to maintain certain types of data, and to make sure your app clearly explains what data your app collects, how it collects that data, all uses of that data, your data retention/deletion policies, and more as described in the guideline
The whole notion that someone could have a legal property interest in personal data collected by others is exceedingly modern. Even the most abstract scholarly work presaging the concept can only be traced back a few decades. Similarly, privacy as a concrete, distinct legal concept is only slightly older. (Notwithstanding the historical narrative gymnastics legal and social policy advocates often perform in their attempts to appeal to tradition.)
Suffice it to say, modern concepts regarding privacy and personal data aren't very useful in understanding banking practices and property regimes that can be traced centuries, if not millennia, in nearly identical forms.