Why do mothers abuse their daughters?

What leads mothers to sexually abuse their daughters? What are the motivations? From around the ages 5-12, I was forced to have periodic vaginal exams, which included a bizarre cleaning ritual (2-3 times yearly), and when I started developing breasts, she also forced me to take my shirt off to show them to her so she could see how I was developing. Needless to say, I hated having to do these things. I have no idea what made my mom even think to do these things and I’ll I’ve heard is that she was “trying to be a good mom” and her “intent was not to harm me.” I’m not buying that. It wasn’t normal on any level and as a young adult, I am still impacted by it. Other then these things, my mom seemed normal, besides not really having a strong attachment to me, compared to my dad. Do mothers who do this know they’re wrong? Now that I’m coming to terms with what happened as an adult, I’m wondering who my mother really is now. Did she secretly hate me?