You said "refs" plural. But it is one (shitty) ref that has complete domination of assignments where the UFC clearly wants one fighter to beat the other: Dean.
You said "biggest fights." But read the 2nd post which shows main events in general have Herb much less (36%) than when the UFC explicitly has an interest in who wins (where it then magically jumps to 80% Herb). For instance, undercard pre-champ O'Malley had way more Herb than main event big fights.
Herb isn't there to simply ref the "biggest fights" because he is one of the "best refs"... he is there specifically to put in the biggest fixes and the stats back that up.