Honest question: Why do some parents don’t feel any guilt for abandoning their families?

Long rant. So a year in a half ago, two months after I turned 18, my older half brother took me to see my late mother after 10 in a half years. He explained to me to lower my expectations and don’t expect mom to be how I want her to me. He kept giving me a blunt, straightforward talk about it. I was nervous but happy to see her. My dad wasn’t too happy with it and for years he refused to let me see her or contact her, but I still did while he wasn’t looking. He one time took my phone and deleted her number and messages I’ve sent her. I wasn’t mad, I had her number memorized. He still didn’t think I was ready to see my mother because he was afraid I wouldn’t be able to handle it, but he let me go but don’t expect her to be excited to see me or be the mother I’ve dreamed her to be. So I went to see her and when I say her, I was excited but nervous and angry. I went to hug her but she stood there like a stool and made a face at me and pulled away. I asked her why did she leave my dad and I. She gave me the most hurtful and brutally honest answer. She said the day I got diagnosed was the worst day of her life and she didn’t wanna deal with having a “special needs” child. She was disappointed because she wanted a normal/smart child. She kept her distance and purposely didn’t show up to my shows or school events. She didn’t even participate in my seventh birthday and she stayed in her room most of the time. Igor diagnosed with autism at age 6. She didn’t wanna deal with a mentally challenged child, so she packed up her things, left us and frankly didn’t regret it. She said leaving me was the best decision she ever made and the best day of her life. And also said that when I tried contacting me, she got very irritated and purposely ignored my calls. The birthday, Christmas and Mother’s Day gifts and cards, she never opened them and threw the cards away and gave the gifts away. She said she didn’t want me and she isn’t sorry for abandoning my dad and I. Wow those words really hurt and I started crying but she didn’t care. She passed away last year and nobody had sympathy for her death. 💔😭💖