Bit pedantic, but the venue is in mainland Europe, by about 15 miles
I don’t have a problem with Istanbul, it’s one of the major air hubs, with regular flights absolutely everywhere. There’s two major airports there, with budget and flag carriers flying to both.
If it were in Barcelona we’d all be looking at flying to anywhere vaguely close or going via Tenerife or wherever. There’s no real difference here and flights would be a fortune (and much pricier when you get there) pretty much everywhere. UEFA aren’t going to hold a final based on where Ryanair fly to from the north west of England