Thats because in MMA there is only one champ per division so the top guys usually have to fight and one loses. In boxing there are multiple belts so you can go undefeated for 3 years and be thought nothing of. But if you do it in MMA its like a rarity. Tito Ortiz has the record for being the longest Light Heavyweight Champ for 3 years. Just 3 years. in boxing a 3 year champ isnt out of the norm but then again you can say who have they fought and maybe find one guy on their resume.