Hype - yes, Hooker talks trash better than Arman, he could attract extra attention to fight
Money - no, I dont think that Arman need money. He is wearing watches that cost times more than his paycheck.
Difficulty - one again, UFC though that he was skilled enough to face champion, now give him Hooker. Mathematically, Hooker has to be same level as Islam But he isnt, not even close.

If I was Tsarukyan, I would have waited for title shot than get involved in a fight that gives nothing (from rating and legacy point of view).