LOL The taxation issue comes up every couple of years, and you see the same hysterical bullshit because people don't understand how taxation works.
Those are not outrageous tax rates.
Australia has a graduated income tax, just like every other western nation.
For example, someone who made $185K income according to that chart would pay $63,450 in tax. The tax is $61,200 for first $180,001 in income, and then $0.45 per every dollar of income above that.
Also, there's taxation treaties between most countries that entitle foreign nationals to refunds from their home tax agency for every penny that they pay while working internationally that's above what they'd normally have to pay in the place they're domiciled.
The actual problem here is the expense for the fighters' teams to travel internationally. I remember reading that the UFC has cut back on some of the comps for coaches/family members.
So unless there's a bunch of members of the same team booked on a specific card in order for the team to pool their expenses, it's not financially feasible for the fighters to go there.