Why don't the migrants organize to obtain better working and living conditions in The Grapes of Wrath? This answer is somewhere in Chapters 17 through 21.
When the Joads arrive at their first Hooverville, Tom speaks to a man about this idea. Tom suggests that people simply stand together and, as a group, refuse to accept the low wages being offered for labor.
The man laughs at Tom and sarcastically says that Tom has got things all figured out by himself. When Tom demands an explanation the man says that others have tried to implement the kind of plan Tom is suggesting.
When Tom asks why the migrants don’t organize, the man says that anyone who talks about organizing is arrested as a troublemaker. (eNotes)
He says that when a group forms there is always a leader that does the talking. The farm owners and the police identify the leader and lock him in jail. If another man takes his place as the leader, he too is arrested in imprisoned.
In this way, organization is suppressed.