Sure there are many homeschooled kids that are above their age-similar peers. However, too often, parents that homeschool want to hide their children from knowledge. They want to control the information that their kids are exposed to. They think its to protect them, but in fact it is too keep them from being their own best versions of themselves. This is also why cults go off on their own.
Another reason is too keep their own family secrets from going out.