Why not?
A major detail you are ignoring here is Apple are the merchant of sale for everything via the App Store (Google at least were not for the Play Store at launch, I do not know if this has changed) so your comparisons do not make sense. The native app universe on iOS is closest to being an Apple run Costco.
I would be very surprised if a fulfilled by Amazon order for a third party seller contained any extra promo materials in the box for similar reasons.
> not to mention that this is 2025, the distinction between "within the app" and "via your website" is pretty meaningless in a bunch of cases.
To you. Not to your end users, and most definitely not to the platform owners.