I think it's easy to doubt these things because it is so hard to wrap your mind around the fact that someone would do something like this to a child. Also, maybe it's easier to doubt/minimize - I know it is for me. There is a weird sense of power in self-blame/self-doubt. If you can tell yourself that it's not real, you can avoid it

I was doubted for many years by many people. I was also called a liar, among other things. Abusers don't want to admit what they have done so they attempt to turn it around on the victims and make the victims question themselves as form of self-protection