In Chapter Two, Piggy does not help with the fire because he is sitting contemplating their situation. The idea that they are stranded, lost without anyone knowing where they are is almost too much to think about. Being a deep thinker, Piggy needs to figure out how to react.
"I bet it's gone tea-time, said Piggy. What do they think they are going to do on the mountain?" (Golding p.38)
He is still functioning on civilized time, when he reminisces about the time of day. Attempting to get his mind wrapped around the situation. He prefers to carefully think about everything before he acts.
When the boys decide to make a signal fire, it does not appear to be an effort that is logical and organized to Piggy, but rather a rambling bunch of wild kids having some fun. Piggy frowns on this disorderly display.
"Then, with the martyred expression of a parent who has to keep up with the senseless ebullience of the children, he picked up the conch, turned toward the forest and began to pick his way over the tumbled scar." (Golding, p. 38)
Piggy prefers to hold onto the conch, which to him represents civilized, orderly behavior.
This chapter starts off with an organized gathering of the boys, and they establish the rules of speaking using the conch. When Ralph suggests building a fire, Jack and the others think this is an exciting and fun idea, so they immediately run off to gather wood. This leaves only Ralph and Piggy, and Piggy thinks the others are just a bunch of unruly kids that have no idea of what they're doing. He wants order to remain in their lives, and he already fears that this won't happen. Piggy grudgingly follows when Ralph goes to help with the fire. Because Piggy is overweight and has asthma, he can't run like the other boys, so he arrives at the fire too late to help. When Jack takes Piggy's glasses to start the fire, Piggy just sits down because he's unable to see without his glasses.