A personal story in regards to your post. My Step Father got custody of my sister, years ago. My mother was suffering from extreme depression, in and out of hospitals for a year. My Step Father was one of the most dangerous men I, or anyone who ever knew him, had ever come across. His motive for having custody was control over my mom, plain and simple. My mom tried, through the court system, as best she could, to regain custody of my sister to no avail. They did finally issue them joint custody as my mom improved through counseling and medication. Before the ink was dry on that order, my Step Dad took my sister down to the woods around Palatka, FL. They lived in a ran down mobile home (back in the woods) for EIGHT years. My sister was six years old at the time. The next time we saw my sister was when she was 14 years old.
We, as a family, looked all over for her, but never found her. I won't repeat what she went through during those years, but she will never recover from the abuse.
This Step father was able to act like quite the charmer in front of judges or anyone he needed to impress. As soon as the doors closed his real self would reappear.
Mothers don't always get custody (contrary to popular belief). My mom improved with the help of doctors, but still she lost her daughter to this ruthless man for the majority of my sisters life. Even when my mom was better, she was in fear of him and confronting a man like this (without police presence) was out of the question.
My mom had a very loving family (parents, aunts) who would have gladly stepped in to care for my sister, but the original Judge saw it fit for her to go with her dad.
This is probably not your every day situation, but Judges DO award custody to fathers (even when the fathers history is far from stellar). I could go on and on, but you get my drift.