Ralph is not in complete control of himself. He is driven by social impulses that he does not seem capable of navigating or controlling. Piggy is a standard-form outcast who defines himself as such, even when trying not to. Ralph can't bond easily with Piggy for the same reason Piggy confesses to Ralph that his name is Piggy. It's social habit.
In addition to what has been mentioned about Piggy's physicality, Ralph spots weakness in Piggy, who whines about his asthma and how they could not have done anything about Simon's death. Piggy exemplifies what T.S. meant when he said, "Between the idea and the reality lies the difference."
Let's be honest. We are all generally reluctant to align ourselves with people we know are going to be mocked and ridiculed, who are not popular and are unappealing. That's Piggy. He is fat, he has asthma, he is disgustingly "caught short" right after Ralph meets him, he wears glasses, he acts like he know better than anyone else, and he is kind of a whiner. Plus his nickname is "Piggy." It doesn't take Ralph long to figure out he is better off to distance himself from this boy; it takes him much longer to realize that, despite Piggy's flaws, he needs the skills and gifts Piggy has if he wants to maintain some sense of order on the island.
Ralph is walking a fine line here. He recognizes Piggy's intellectual assets, but recognizes that the balance of power is tenuous at best and in order to maintain his control of the boys, he has be distanced from the rather repellent Piggy. These are all young, frightened, and impressionable boys, and Ralph recognizes that he could fall into the trap of "guilty (or weird) by association" if he too closely aligns himself with Piggy. It is interesting to notice how their relationships ebbs and flows throughout the novel. As Ralph grows up, so does his connection to Piggy, which is another example of the difference between civilization and savagery in the novel.
I agree with the first post. Piggy has nothing going for him. All his attributes are ones that get you teased unmercifully when you are that age. Ralph is one of the "cool kids." If he makes friends with Piggy, he's going to lose his image as a cool person and no one will want to follow him anymore.
So I think there are two things going on:
- Ralph knows that the other boys won't follow him if he is friends with Piggy.
- Ralph is personally repelled by Piggy because Piggy is a brainy geek who's too fat and can't do anything physical because of his asthma.
i feel its because he see's piggy as different and a complainer.