Appeal to tradition is a fallacy in logic, but laws are not made using pure logic. Laws are made when some group with sufficient political power wants them to be made, and such groups are often driven by tradition, what they perceive to be tradition.
> Or perhaps more importantly, what fuels the belief that they are at all in the position to do something about it?
The European Union is a government; it makes and enforces laws. In this case, it has made a law called the Digital Markets Act which addresses certain types of gatekeeping behavior by large tech companies including Apple. Some readings of this law I've seen forbid Apple from charging fees for distributing apps outside its store and from using any legal workarounds to circumvent that prohibition. It remains to be seen how EU regulators and courts will interpret it.
Your comment makes several references to "IP", but isn't clear about what IP is involved. Is it necessary to use inventions patented by Apple to write an app that runs on an iPhone? Is it necessary to know Apple's trade secrets (aside from things like signing keys that exist for the sole purpose of gatekeeping)? Does it require making copies of things Apple holds copyright to?
