For me at least, it's a general dislike of the wider educational system. My parents taught me to read, play chess, multiply, and write in cursive before elementary school. I didn't really learn anything at preschool or kindergarten, and I imagine daycare would be worse for my educational development. Maybe it's useful for social development? but at least for me I was always pretty independent (even in kindergarten) from the other kids. Not in an isolated way, I just preferred doing my own thing.