Even though they're evil and unable to show affection, I have some craving for the romance I've been seeing in fiction and imagining.
I want to feel her warmth, be able to share my worries with someone, share my everyday life and be able to create some special moments together. I'd even like to take care of her (not to a cucked level) to feel a purpose in my life.
Of course my biological needs are also an important reason. It must be great to do it with someone and instead of suffering of post nut clarity just cuddle and get praised for doing it right. Maybe I'd even like to make a child but I don't know if making another person an incel would be right.