What's your source for that? Apple subscriptions also dwarf the next closest provider. I don't think Apple users care about paying once or more than once so long as they have access on all their devices.
My source is myself! I am an App Store developer. Did you miss the part where I said, "Last month I finally gave in and made my Mac and iOS apps a universal purchase instead of separate purchases"? This was because customers were constantly confused and complaining about it.
I can see some frustration with idea of paying for the app full cost separately. But I think I would be less annoyed if I can pay for both in a single transaction. Even if it wasn't at a discount for the bundle, $10 for both.
Apple doesn't support this: https://lapcatsoftware.com/articles/2023/12/4.html