Johnny refuses to see his mother when he is in the hospital because he feels that she does not care about him.
Johnny Cade came from a troubled home where he suffered abuse at the hands of his father and was neglected by his mother. We learn early on that Johnny does not like to go home, and that his father often beats him and his mother blames him.
His father was always beating him up, and his mother ignored him, except when she was hacked off at something, and then you could hear her yelling at him clear down at our house. I think he hated that worse than getting whipped. (Ch. 1)
This is what makes it so heartbreaking when he gets jumped by a group of Socs. Johnny is even more nervous after that, afraid of his own shadow. He only has the gang to look out for him, since as Pony says his father is an alcoholic and his mother is a “selfish slob” (Ch. 3).
When the Socs jump Johnny and Pony in the park, he panics. After accidentally killing a Soc, Bob, Johnny and Pony went on the run. The killing was self-defense and Johnny was trying to save Pony’s life. He did not feel that anyone would understand. Johnny risked his life to help the children in the church as well.
When Johnny is in the hospital, his friends are all there trying to visit him. The doctor allows it because he knows Johnny is dying and it will not make a difference. However, when Johnny’s mother shows up, he refuses to see her.
"I said I don't want to see her." His voice was rising. "She's probably come to tell me about all the trouble I'm causing her and about how glad her and the old man'll be when I'm dead. Well, tell her to leave me alone. For once" ---his voice broke--- "for once just to leave me alone." (Ch. 10)
Johnny feels that his mother is there out of obligation, not because she loves him. He is afraid that she will once again blame him, and he cannot face it. He does not feel love for his mother at that moment. He is in pain and weak, and cannot bear to face her particular demons.
As the incident with his mother in the hospital shows, Johnny’s real family is his gang. The greasers have convinced hospital staff that they are his family, and they are right. Johnny’s parents are not the ones who care about him or take care of him. His friends do that.