It is quite possible that Apple is, technically, breaking EU law but the Commission are letting them get away with it because they have more important things to deal with. With no consumer outrage and no real local competitor to protect from a foreign predator there is no political gain from action.

However competition law applies uniformly across the EU so it is easy to comply with, if you choose so. A more complex situation exists with Facebook. To follow a variety of applicable national and state law they would have to an extraordinarily large amount of legal resources familiar with the respective intricacies and probably create national variations of their product. This is the kind of thing that holds back European companies but in this case it protects FB, because the Commission (the only institution with enough political clout and resources to take action) is only going to address EU-wide issues, not a bag of a dozen different issues. So it is rational for FB to mostly ignore the law, which in reality they chose to do.