Of course you would take the fight. So would I. We have nothing to lose, do we? We get our ass kicked for one night and we get paid. Losing to a MMA fighter such high calibre is nothing to be ashamed about as well. We earn extra income for basically getting whupped.
However, our day job ain't MMA fighting. These people need the money for survival. Their career span is short, and they need to earn as much as possible before retiring/finding a lower pay job. If they take high-risk fights and lose, not only would they drop down ranking wise, their career might soon be in jeopardy and they would find themselves in the lower-paying leagues again. Try thinking from the fighters' perspective.
Mayweather and Pacquiao both made up excuses to not fight each other. They do not want to fight each other, and neither can they be forced to fight each other as boxing has a different organisation structure to that of UFC. However, UFC can make the fighters fight each other. Otherwise, just fire them. I'm sure no UFC fighter wants to be cut, considering the monopoly hold UFC has on the MMA industry. So what is preventing the fighters from earning more money?
I just googled XARM to get a clue what you are talking about. If you are considering watching that over MMA...