No surgery is perfect and there are failures like over healing and improper healing. That said, those are relatively rare. I suspect many of the "failed surgeries" are the result of false expectations. You don't just pay the money and walk out with a feminine voice. The proper path is speech therapy to learn what you need and if you need it. Next come studying the surgeons to find the procedure you need followed by the surgery. After that, you may need additional speech therapy to learn the proper way to use the new voice.
In my case, even after surgery my chest voice is 130-140 HZ which is still in the male range. I need to use the head voice and when I do, I have a very comfortable 220 HZ voice extending to over 500 HZ. If somebody is unable to use the head voice and they had a starting voice like mine, they would consider the surgery to be a failure. I consider it to be a success because my pre surgical head voice was 130 HZ.
Voice surgery isn't a quick easy fix. It's a combination of speech therapy and surgery and when done correctly, can do amazing things. It's far from a solution for many and many can do just as well without the risk using only speech therapy.