A petty move like this clearly shows that Apple as a company has nothing valuable to offer developers. Shutting down "sign in" options shows that internally, Apple is looking for a way to hurt Epic in a manner that hurts the most but they are coming up short. Although iOS accounts for over one-thirds of Fortnite's 360million users, Epic has already made the brave decision to let that portion of revenue go and nothing…
I don't think this is a specific targeted thing. It just comes with the general deactivation of the Epic account. It's the same as the whole "Apple is banning all apps made with Unreal Engine!" which was a poor take on the issue. (What actually happened was Apple un-approved Epic's license, which had a cascading effect because Unreal Engine was signed under the same license, and so software dependent on Unreal Engine…
Developers using Unreal Engine certainly do not sign their app with Epic's credentials.