Answer :
Because Candy is old, he is seen as lower in society and unimportant. he is metaphorically associated with his dog, who is also old and is put down, which foreshadows Candy's destiny.\\ chapter 2 page 26 in my version-
"You was poking your big ears into our business. I don't like nobody to get nosey" Says George to Candy (described as the old man/swamper) It shows the way that other men on the ranch treat Candy, with little respect, because of prejudice.
Candy replies a few lines down
"A guy on the ranch don't never listen nor he don't ast no questions"
This shows that most ranch men, apart from George and Lennie, have no friendships and are generally lonely since they have no business or somebody to talk to.
Later on, page 48, Carlson says to Candy
"God awmighty, that dog stinks. Get him outta here, Candy! I don't know nothing that stinks as bad as an old dog. You gotta get him out."
The way that Carlson insists getting rid of Candy's old dog shows little care towards the emotional attachment Candy has for his dog.
This shows some reflection of society at that time because animals and the elderly were seen together at the bottom of society because they are both conveyed as past their best.
