In Of Mice and Men, why is Crooks so lonely?

Crooks is the lively black stable-hand on the ranch with a crooked back, who is extremely lonely because he suffers from racial discrimination and is segregated from the other white workers on the farm. Since Crooks is the only black worker on the ranch, he is not allowed to live in the bunkhouse and is forced to reside in a small room attached to the barn, where he spends the majority of his time alone. In chapter 4, Crooks laments about his loneliness by telling Lennie,

"S’pose you didn’t have nobody. S’pose you couldn’t go into the bunkhouse and play rummy ‘cause you was black. How’d you like that? S’pose you had to sit out here an’ read books. Sure you could play horseshoes till it got dark, but then you got to read books. Books ain’t no good. A guy needs somebody—to be near him...A guy goes nuts if he ain’t got nobody. Don’t make no difference who the guy is, long’s he’s with you. I tell ya...I tell ya a guy gets too lonely an’ he gets sick" (Steinbeck, 36).

Crooks suffers because he is treated as an outcast and forced to play card games and read books by himself instead of socializing with the other workers. Crooks is the unfortunate victim of racial discrimination and is forced to live separately from the other workers, which is the main reason he is lonely.

Crooks is an older man whose body is literally bent to the left; he is a "cripple," in Steinbeck's words. He lives by himself in his own bunk in the harness room with a few spartan possessions, and his attitude is aloof and distant from the other men on the ranch. He takes care of the horses on the ranch. 
Crooks is lonely because he is the only African-American man for miles around. While he was born in California, where his father owned a chicken ranch, he has always felt different and unaccepted because of his race. He has become used to being alone and lonely, but he also has an element of bitterness. He relates well to Lennie, though Crooks is initially hostile to Lennie and taunts Lennie by telling him George will never come home. Crooks begins to become excited about living with Lennie and George on the ranch they plan to start, but this excitement is only a temporary break in his loneliness.