Apps in certain categories (ebooks, music, video, news) can choose to not support purchasing at all in apps, or to use in-app purchases.
Outside these categories (eg a email account as a service, group classes) you are expected to always have in app purchasing.
There have been interesting ways people have explored getting around this, but obviously Apple thinks they should be paid what they are contractually obligated.
Having control of distribution means it is easy on Apple’s side to solve disagreements. You only see it brought to lawsuit by the other side (e.g. Epic’s lost case in the US)
Outside these categories (eg a email account as a service, group classes) you are expected to always have in app purchasing.
There have been interesting ways people have explored getting around this, but obviously Apple thinks they should be paid what they are contractually obligated.
Having control of distribution means it is easy on Apple’s side to solve disagreements. You only see it brought to lawsuit by the other side (e.g. Epic’s lost case in the US)