If Apple didn’t offer in app purchases developers would be screaming.
Now perhaps, but Apple didn't have to offer it in the first place.
Worth considering that it could be a better and different place had that happened.
As you know, what Apple does has a large impact on where things go in these spaces.
If Apple decided non IAP was simply "better" for its customers, devs would fall in line.
It would be a remarkably "Apple" (the old Apple at least) move actually.
All that aside, I still maintain that they should be requiring a pay one time option* from all Apps, even if they offer IAP.
*again, this could have limitations by iOS version(s)