I don't care that my dad is dying of a disease and my mom is showing signs of alzheimers,
Why don't you care about the health of your parents?
He has always been a shitty father, I have no reason to feel sad.
You may have had negative experiences with your parents. However, you should care about their medical conditions. If you don't you will regret your choices one day, when you have healed from the past.
I'm not sad. I don't want to talk about this. I don't care about them.
While your parents aren't your responsibility, they may not have other people to take care for them or help them, so I do hope you help them get a caretaker if you aren't able to take care of them. Even if they were not great parents, they still helped you grow up and reach whatever you have reached today.