Crooks and Candy are practically charity cases. Candy lost one hand in farm machine and Crooks had his spine badly injured by a horse. At the time in which the events of the story occur, employers had no legal liability for work injuries. (Since then there has been considerable legislation mandating workman's compensation insurance, and there are other federal measures protecting people who are no longer capable of supporting themselves.) The owner of the ranch must have felt some moral responsibility for the work accidents , because he kept these two men on and gave them jobs to do. But both of them feel terribly insecure. They are well aware of the fact that once they are unable to perform their simple chores they will be discharged. That is why Candy is so anxious to become a partner with George and Lennie in their project to buy a small farm and be self-sufficient. It also explains why Crooks wants to get in on the project himself once he hears about it. Neither of them has any other viable options. It is only a matter of time before they will become useless to the hard-hearted, practical-minded boss, who shows himself for what he is when he first meets George and Lennie in Chapter 2.
These men's handicaps have affected their characters. They have to be humble, courteous, industrious, accommodating, and inconspicuous. Crooks has learned to stay by himself and entertain himself because all the men are automatically prejudiced against him for being black. However, he has an advantage over Candy. Crooks is quite capable of working with horses. This is understandable and rather touching. He has to make friends with the horses because he has no human friends. Not only that, but Crooks can save the owner money by repairing all the equipment used for working with horses. Candy is white and is accepted in the bunkhouse, although he obviously has a lower status than the other men; but his physical handicap is very serious. He is supposed to do sweeping, mopping, and scrubbing--and how can he do such tasks with only one hand?
Candy is speaking for all working men who get injured on the job when he tells George:
"I got hurt four years ago. They'll can me purty soon. Jus' as soon as I can't swamp out no bunkhouses they'll put me on the county. . . . You seen what they done to my dog tonight? They says he wasn't no good to himself nor nobody else. When they can me here I wisht somebody'd shoot me. But they won't do nothing like that. I won't have no place to go, an' I can't get no more jobs."
The ranch owner gave him $250 as a token compensation when he lost his hand. Crooks probably got nothing at all, and he may not receive any salary but is expected to be grateful to have a roof over his head and regular grub.
Both of these men have been broken psychologically as well as physically. They don't expect any kindness, and they don't receive any. They are both uneducated. They accept conditions as they find them, without speculating that something might be done to improve them.
(addition to my first answer)
Candy also craves an escape from the lonliness he feels at the ranch and this is one of the reasons he is so eager to join George and Lennie on the venture of buying "their dream farm". He offers all of his life savings to go in with them as partners. Again, touching on the everpresent themes of "Lonliness and Friendship" in this novel.
Crooks and Candy are similar in that they are both made to feel like outsiders on the ranch.
Crooks is the only black man on the ranch during a time period of racial discrimination. Therefore, he comes from a background of being treated differently due to his skin color. However, he is also treated differently because of the deformity of his back, hence the name "Crooks". He is made to feel inferior and isolated because of these two factors. He is jealous of the relationship that George and Lennie share. He actually speaks about "not having any friends and feeling lonely." Like he says in the book, he is allowed to play horseshoes during the daytime with the other men, but when the sun falls he is forced to go to the barn (where his room is) and sit there alone and read, while the other ranch hands retire inside to play a game of cards.
Candy also feels "left out" due to his old age and his missing hand (lost in an accident on the ranch). He feels isolated, because they don't let him do as much on the ranch anymore. He is actually a parallel character to his aging dog (that is later shot by a ranch hand). He knows that his time on the ranch is limited due to these physical limitations and feels resentment because of the fact that he has been employed at the ranch since he was a young man.