Payment processing alone would cost Apple that much. You easily lose 1.5%-2% in payment fees and another 2% in handling fraud and customer support queries about payments.
For example, if a payment for an app is $1.99, Apple now takes $0.60. If a customer calls support to ask a question about the purchase it can cost anywhere from $15 to $30 in call center fees, so it takes 50 purchases to make good on that. If you lower that to a $0.06 take apple would have to make 500 sales for every phone call to support.
People don't realise good customer support is very expensive.
This discussion is about Epic charging for in-app things outside of Apple's control. So apple can't use the argument that they have costs (support, payment) for those transactions.
If I buy a hat in the Epic store (and pay to epic) I don’t see why it would be very different.
Should it matter if I make the purchase in Safari or in another app?
Also: let’s forget the apps for a while. Assume I buy a navigation app for $10 on the App Store and then I visit a website and purchase gps maps for 3 countries to use in the app, for $100 each. Apple isn’t involved in that transaction. Should they claim a cut of the $300 because I can use the maps in the app?