I think the only problem with a world tour would be audience attendance and athlete safety.
Some of the middle eastern countries and asian countries love BBing and would be all for it. Though I don't know how safe the event would be there. Other safer countries you might battle to get a decent audience as BBing isn't mainstream.
I think the biggest factor is revenue. Aren't all the major sponsors American and its most I don't think they'd bring in the same amount of cash if it were sent elsewhere. That said it would be a great bonus for the sport to have it toured around the world. Maybe they should send it somewhere else once every 4 years or something.