How and why is Piggy considered by the others to be an outsider?

Piggy is an outsider for many reasons. His health is one. Boys like Ralph are strong and healthy. They are confident in their ability to act. By contrast, Piggy is fat and has asthma. He wears glasses, and his mom has been very protective of him, making him hesitant to act. However, he's also an outsider because he is fundamentally an intellectual. He lives in his mind, while the other boys in their bodies or the community. That makes him seem weird to them.