Why do so many great MMA fighters have multiple losses on their record compared to boxers?

It seems to me that the truly great MMA fighters tend to have multiple/more losses on their records when compared to boxers, where the truly great ones tend to have none or one or two defeats only.
While it is true that a higher percentage of MMA fighters have losses on their record than boxers, this is most likely due to the fact that MMA fighters do not fight as much as boxers.  [3]  Furthermore, the purse for boxers is just bigger, as they can make significantly more money from just one fight than an MMA fighter can in a year.  [3]  Boxing also has different organizations and belts, with mandatory challengers getting to fight for belts, whereas in MMA, Dana White is like a dictator, deciding who fights who and when.  [4]
MMA fighters have multiple losses on their records for several reasons. First, MMA matches do not end after three rounds like professional boxing matches, but instead go on until a fighter yells “tap” or is knocked out [1]. Second, there are many MMA fighters who have lost many times, but keep coming back and improving to be ranked at the top [1]. Finally, unlike in boxing, there is not a standard number of fights that make up a fighter's record [2].