Some WG's will decide to hide the feedback even if there was only 1 negative. Possibly, the feeling that 1 negative can carry a lot of weight, when a lot of profiles have none. Even though hiding the feedback is even more of a warning sign for most punters.
I believe the other main reason feedback gets hidden is when a punter has mentioned receiving bareback from that WG. But she is trying to deny that in her enjoys or Q&A's.