Apple seems to have the position that if a company is going to start publishing apps with non allowed systems once that they will probably do it again with other apps. Epic has had the choice to conform to terms (they were not even losing money on in-app unlike the content streaming folks), even if that means removing all mention of in-app and have yet to do so. More or less Apple did the same thing to Facebook in the past for the profile abuse. Facebook just hadn’t prewarned their marketing team they were violating terms of service on purpose.

Edit: not that Epic isn’t right to sue to see if they can get their way, just that they should have sued without violating current terms. My personal belief is that much of the 30% goes to gift card promotions and markup which brings in funds for all developers.