I've been trying to wrap my head around why Epic would shoulder-tackle Apple in the space of app stores, when they have their own app store. Naively, I've been thinking that any ruling adverse to Apple here also impacts Epic's business model---if the government caps app store revenue cuts at, say, 10%, that's a slice off the top of what Epic can charge developers going through its store, too.
But Epic is a game publisher first, app store owner second. A fair and regulated market is a win for them, because it decreases the barriers to competition in the app store space while, on average, probably diminishing store owner cuts, which benefits developers, of which Epic is one. So a more regulated market is a net positive for them.