Hello!
Here are my thoughts from when I read Lord of the Flies:
Piggy is routinely taunted by the other boys because of his size.
Piggy is demonstrably more intellectual than all the other boys, almost certainly making them insecure as a result of their inferiority.
The boys' insecurities prompt them to try to make themselves feel better by bullying Piggy; they pick on his lack of physical strength and power.
They decide to illuminate his weaknesses because they want to see themselves as better than others.
I hope this helps you! (: