It's pretty simple. The judge ordered Apple to file a written brief and to send a relevant executive to court to explain why Epic's app (Fortnite) was still excluded from the U.S. App Store. If the reason was solely because Fortnite offers in-app purchase options via Web links, and/or because Epic Games sued Apple to resolve that issue, then that reason would clearly violate the judge's orders. Apple lost that issue at trial and in appeals. Apple cannot exclude apps solely on that basis — or on the basis that a party sued Apple to resolve that particular point of contention. If Apple has some other valid, legal reason to exclude a developer's app from the App Store, that's a different matter.
Apple apparently didn't have some other valid reason to exclude Fortnite from the U.S. App Store, or at least Apple wasn't prepared to explain what other valid reason(s) it has if it has one. It has to treat Epic Games (Sweden) just as it would treat Developer XYZ — and consistent with the court's rulings. Apple's lawyers presumably advised Apple's management they needed a "damn good reason" to exclude Fortnite that's unrelated to the in-app purchase issue and also unrelated to any legal actions Epic Games took related to resolving that particular issue. I can't think of any "damn good reason," and it seems neither could Apple's management.
Interestingly the European Union has helped Epic Games maintain a developer presence in Apple's App Store, so it's that much easier for Epic Games to get back in. But that's Apple's fault, really. Apple already cancelled Epic Games' previous developer account. But since Apple violated EU competition laws it had to let Epic Games (Sweden) in. Now Apple apparently doesn't have a valid, legal reason to exclude a Fortnite submission from Epic Games (Sweden) in the U.S. App Store. In short, don't violate laws. If you do, bad things may happen (from your corporate point of view).