It's been in Europe 3 times
It's been in North America 3 times
It's been in Asia 1 time
It's never been in Africa, Oceania or South America.
You have unintentionally made a good point here. Let's look at top 100 of the most competitive event (3x3x3 average):
Europe: 37 people
Asia: 34 people
North America: 26 people
Oceania: 2 people (Kirt's close, but no cigar, sorry)
South America: 1 person (he's from Brazil)
Africa: 0 people
So Worlds has always been on a continent with a lot of good cubers. In fact, looking at this list, I think we need another Asian competition - they have been sorely underrepresented. On a world scale, Oceania and South America are really not competitive at all (and Africa's not even on the radar, which is why I joked about them). There's Feliks, yes, but he's really way ahead of the curve as far as Oceanians go. What the bottom three continents need are not Worlds competitions, but more local competitions and more outreach to potential local cubers to get them interested and practicing.
If we want to look at "what's good for the community as a whole", as DeeDubb said, we should be holding Worlds in places that let as many good cubers as possible travel to the occasional one, even if they can't fly halfway across the world. Brazil actually makes it harder for top people to compete if they don't have the resources or money to fly that far. This isn't a personal argument as I am rather unlikely to attend Worlds no matter where it is. If you are a top 100 3x3x3 solver, and not Gabriel Dechichi Barbar, you WILL have to fly from your home country to a different continent to attend Worlds.