Mario's going to need some way to take the edge off all his aggression from that unsuccessful foray into the dating world. What better way to let off steam than beating some guy to death in a mixed martial arts duel?
Take the typical cast of characters (Peach, Baby Luigi, Boo, etc.) and throw them in the ring with an arsenal of new, deadlier moves, and you've got a hit. In fact, why not just option the entire cast of Super Smash Bros. over to Mario's Manly MMA Beatfest and call it a day. Those characters have been itching for something more hardcore after spending years wailing on one another with flowers and paper fans in Smash Bros.