They might try those things.

But what if the EU just turns around and fines them x% of global revenue for that?

The EU law could effectively force Apple to open up. Ex: who says the law only applies to EU sim cards?

What if, the law instead applied to EU citizens, and if an EU citizen happens to have an American sim card, well then that's Apple's problem and they have to allow US sim cards to side load.

Playing clever games could just result in billions in fines and Apple being ordered to change anyway.