Adopted by my abuser

I was adopted from an orphanage when I was a baby by my single mom. My mom was suicidal and abusive throughout my childhood. She’d hit me super hard, drag me around, scream in my face, sexually harass me, and she even fondled me down there once. She attempted suicide multiple times when I was a child and even blamed me for one of them. As a teenager I was raped and couldn’t even tell my only parent because I was afraid of how she’d react (I tried telling her about the time my preschool teacher assaulted me and she didn’t care). My mom was so cold and unstable. She was clearly not ready to have a kid. I wonder why she even adopted me in the first place.