[Grustaf]

Reasonable people may argue that they have a monopoly on iOS apps, which could be problematic, but they don't have anything even remotely approximating a monopoly on video calling or messaging apps, which is what we are talking about here.

They also don't have any kind of monopoly on TV or music streaming, so there would be nothing wrong (and certainly nothing illegal) with keeping Apple Music and Apple TV exclusive to their platforms, so clearly they believe they will make more money by making them cross platform. Presumably it's the same with Facetime.