I wonder how many big-name fighters are reluctant to fight in the UK or Australia. A fighter is supposed to be finely-tuned and ready to perform at his best in the cage. To do that, he wants everything to be as controlled, stress-free and familiar as possible.
But in the week or two before the fight, he's got to take a monster plane ride and pretty much reverse his body clock. He knows that whatever happens in the fight, it'll take a couple more days travel to get back home. The distance, time spent away, unfamiliarity of his surroundings and removal from his family and support systems may make him homesick and **** up his sleeping pattern. And he might have to fight at a weird time for American TV schedules.
It's not like he'd think "I always wanted to visit Australia!" either. He's not a tourist, before the fight he's got shitloads of stuff to do and after the fight he wants to get back to his family.
Maybe I'm completely wrong, but I can see why big-name North American fighters would be reluctant to volunteer.