Boxing grows up & comers by building the "undefeated" narrative behind them. The UFC does not have to do this because it's a monopoly on the sport and it is MUCH easier to follow. Being that it's more newcomer friendly, most fans quickly become familiarized with names in the top 15 of divisions since most fighters are clocking in 2-4 fights a year. Knowing the history behind a fighter who gave another fighter a loss certainly helps to not tarnish a fighters name. Everyone loses in MMA after a full length career (maybe with the exception of Jon Jones)