Probably because the Dark Tournament is the setting for the plot, rather than the plot. YYH is probably one in a small handful of animu to not turn into an autistic spaghetti 'fest. It didn't lose itself in the "it's a tourney guise!" and proceeded to shoehorn a metric crapton of one-shot characters you'd never see again and provided nothing to the plot.
With the monkey paw in hand, I give you my counter argument:
Fusion would be a whole lot of Steven Universe references. Yes, that means everyone who fuses is fucking gay for the other person, very deep down. Yes, a lot of "Vegeta being in a blastproof closet" jokes would be made.
Do you really want that?