Are court systems biased towards fathers?

Okay since I didn't want to make a long ass title this is specific to COURT custody cases of a fathers kids.

Over this weekend I found out I had an older half-brother named Carson. My dad didn't know about carson until he was 8, and at that time my father was fighting for my sister and i.

Even though my father was more financially and mentally stable, my mother somehow won the custody agreement. And my dad never fought for carson because he was scared to go through the process again and lose, possibly losing the little contact with his son he was allowed.

I also did a little research:

In Canada 79.3% of mothers receive exclusive custody.

6.6% of fathers receive exclusive custody.

12.7% of parents have shared custody.

Bonus question: do you think it's fair? Why or why not.