The thing is the USA is one country, while the European countries are technically separate, so they can do that. Yeah, Chinese airlines tend to completely dominate longhaul.
As for the original question,
As far as I know in the real world a European airline can open up bases and flights to the States, for instance, without any restrictions. Why isn’t it the case in here?
I’m really confused as to what you mean here. I cannot think of a European airline that has based their aircraft in the US that has operated to anywhere but the EU. Some examples:
- Norwegian’s bases in America only operate to EU destinations where they already have narrowbody bases.
- Air France’s LAX only really operates to French destinations (since PPT is still technically France)
- Qantas’s (I know it’s not EU but) operates its LAX-JFK as a scissor of their Australian feeders. It cannot book people on the t-cons, only continuing traffic from its transpacifics.
AFAIK it’s prohibited for foreign airlines to operate domestic pax in the US under their law.
And yeah, while I would argue the USA and China are overpowered geopolitically in AS, a) there tend to be more airlines and more competition, and b) that’s how it is in IRL anyways.