When we are first introduced to Granddaddy Cain, we are told that "folks like to go for him ... because he’s so tall and quiet and like a king. And people just can’t stand it." The implication here is that people "can't stand" Granddaddy Cain for three main reasons. The first reason is that he is so big and tall. Sometimes people like "to go for" or attack big people because they feel threatened by them. It seems that people "can't stand" and "go for" Granddaddy Cain because they feel threatened by how big and tall he is. Perhaps Granddaddy Cain makes these people feel small by comparison, thus also insecure. It is understandable that people might dislike a person if that person, albeit through no fault of their own, makes them feel insecure.
The second reason why people "can't stand" Granddaddy Cain is because he seems to walk around "like a king." This suggests that other people might think that Granddaddy Cain is arrogant. To these other people it might look as if Granddaddy Cain believes himself to be better than everybody else, as if he considers himself a king and everybody else his subjects, or inferiors.
The third reason why people "can't stand" Granddaddy Cain is because he is so quiet. People perhaps interpret this quietness as more evidence of his arrogance. Perhaps they think that Granddaddy Cain's quietness is an indication that he believes it is beneath him to talk to or explain himself to these people. Granddaddy Cain's quietness also perhaps makes him seem inscrutable, which in turn possibly makes other people suspicious of him. His quietness implies that he is not friendly or sociable, and people in general are more likely to feel hostile towards unfriendly and unsociable people.