Yes, and they cover for each other.
If you get a bad diagnosis and treatment and then see someone else for a different outcome, it’s very unlikely that Dr. Successor will tell you anything negative about his/her predecessor. Doing so is viewed as unprofessional behavior – undermining patient trust, compromising care, and blame-shifting. Also, because medical practice is as much an art as a science, it’s considered wise not to second-guess a colleague’s judgment and to assume it was made responsibly.
There are arguments pro/con keeping quiet v. sharing observations. Personally, I dislike being treated like a child and will always want more information.