Epic's first-party games are often a showcase / development driver for new versions of UE, though (the way Unreal, the game, first popularized UE, the engine). If Epic can't publish their own games on iOS anymore, they would have less incentive/ability to iterate UE on that platform even if that license wasn't canceled.

It's a loss for cross-platform gaming altogether. Apple just really doesn't give a damn about their users =/