I would think there could be a couple of reasons for that, for one there wasnt alot of fighters that talked about fixed fights in pride while pride was still up and running as far as I know it wasnt until pride was a sinking ship that stories started to emerge, even now there are numerous fights that were largely assumed to be fixed in pride that people havent come clean about, Leko vs Ogawa comes to mind.
Zuffa and now WME have very strong legal teams, outside of the fighters that have thrown fights((if there have been in the UFC)) who else can say so affirmatively that for sure there has been, coming out and blabbing to the media about something that is very slanderous on the strength of word of mouth is grounds to be sued
we all know how Zuffa were not very fond of releasing big name fighters they had under contract out of the goodness of their heart....now look to what happened with Wand...he came out and it looked very much like he was going to be talking about fight fixing and immediately the UFC sued him which put a gag order on him I believe....instead of the suit actually going thru they came to an agreement and he was released from his contract without another word towards what he had been alluding that he was going to come out and talk about
I dont like to think of the UFC fixing fights and Im definately not a guy that jumps all over screaming fixed fight at the first thing that isnt the norm. but that situation with Wand was very very suspicious/telling IMO
also IMO I would think that over time there have been some fixes in the UFC with the majority of those being in the earlier stages of the UFC's history, possibly even involving Wand ((during his first run)) I think after the UFC gained more and more popularity it would become both harder and more dangerous to do