This isn't a question with a one-size-fits-all answer. It seems pretty clear that for you and your family, preschool isn't necessary, and you're comfortable the way things are. Don't feel any pressure to change that if you don't want to.
For me, preschool was absolutely necessary. Unlike you, I had a very strong desire to send my child off when I was at home. For my sanity, I needed time alone. I have always craved solitude and motherhood didn't change that. Both my kids were very eager to go to preschool (if they hadn't been, I would have reconsidered) and thrived there. It was good for all of us.
For me, preschool was absolutely necessary. Unlike you, I had a very strong desire to send my child off when I was at home. For my sanity, I needed time alone. I have always craved solitude and motherhood didn't change that. Both my kids were very eager to go to preschool (if they hadn't been, I would have reconsidered) and thrived there. It was good for all of us.