After two days of being available on iOS, Apple has shut down popular screen modifying app, f.lux. The app which was previously available on jailbroken devices was made available through ‘side loading’, which was introduced in iOS 9 to allow users to download apps that aren’t available on the iOS App Store.
From the outside it looks like the developers behind f.lux did nothing wrong. However, the issue is that the f.lux developers did not open source their code. The app was precompiled and users were asked to download a master file and that was about it. Of course, you needed to have Xcode installed on your Mac.
Another reason may be because the application was so popular and Apple did not want that many users installing an application that would’ve never made it to the App Store.
The developers go more in depth here, but basically, Apple did not tell them why they shut it down, but their hands were tied.