By the time they reach the gate of Buchenwald, the prisoners have so long become inured to the slow death that is their lives, they have begun to focus desperately on staying alive and looking out only for themselves. Elie too has seen young men trying to keep bread from their fathers or sometimes abandoning the care of the older men to ensure that they would be able to stay alive. He is desperate not to sink to that level although he contemplates it repeatedly.
As his father falls ill with dysentery, the other prisoners are well aware that he basically has no hope of survival and is a drain on resources that could be used for others. Even the doctors all tell Elie to simply let him die and to stop trying to save him. The other inmates avoid contact with him as it also requires an emotional investment to care about others; this is one that they are not willing to make with someone they know is going to die.