It is not because Epic wanted better terms, it is HOW they went about it. They violated an agreement they made with Apple by submitting an app that met Apple's guidelines so that it would be approved. After the app was approved and live, they made a back-end change on Epic's side, which redirected the app to their (Epic's) payment source. An action they KNEW would get them banned, but they did it anyway. They were unscrupulous and purposefully violated rules they didn't agree with. There are correct methods to dispute things, and there are incorrect ways. Epic chose the incorrect way to force Apple to the table.
To your point, from page 178-9 of the Judge's opinion:
Epic Games never showed why it had to breach its agreements to challenge the conduct litigated. Two parallel antitrust actions prove the contrary. Apple had contractual rights to act as it did. It merely enforced those rights as plaintiff’s own internal documents show Epic Games expected.