When a World Cup game is played in California and a fan from Europe wants to attend that game, a long-haul flight has to be booked to in order to watch that game assuming that the fan won the ticket lottery beforehand.
What exactly is the problem now with three countries co-hosting a World Cup? If a fan from Mexico wants to watch the final and the final takes place in the US, the fan has to travel to the US the same way a fan from Europe has to travel to the US. What is the difference in the planning procedure for any fan from any place when they decide to watch a game?
Visa could be one reason, but I think that the US won't make it unnecessarily hard to get one. If a fan from Washington wants to watch a game in California, that is a hell of a ride. Except for the visa procedure, traveling from Washington to California is at least as exhausting as traveling from Mexico to California unless you are from the deepest South of Mexico.
If this is not a crazy national team fan, than this guy visits few games, probably stay in a city abroad for few days and fly away. Each tournament - this is +2 weeks non-stop games routine. I doubt that an average man can afford to go for a +2 weeks holiday just to watch favourite team play, plus buy tickets, that often cost 50+ bucks for shitty seats during prelims. I think such expenses are unacceptable for an average fan, that is why few games/few days is enough for him.
I have travelled from Europe to US and have visited Mexico via cruise about 5 years ago. I dont remember visa being a problem and cost a lot. Plane tickets wasnt expensive either, as I have bought them months before the flight. Hotels ate most of the budget, but it was a high season in Miami.