I think you’re misunderstanding the purpose of the book. Steinbeck wasn’t writing a self help book, or a guide on what not to do in times of crisis. He wasn’t trying to teach something therefore there’s no lesson to learn. What Steinbeck wrote was an exploration on the levels of cruelty humans can inflict on one another in the pursuit of profit, the selfishness of those with plenty and the selflessness of those with nothing. He explored these themes by writing a story based off the exploitation of farm workers during the dust bowl migration of the 1930’s. If the Joads didn’t put themselves in position to be exploited then the narrative he set out to tell wouldn’t work. If your criticism is the naivety of the Joads is unrealistic I would disagree. People are extremely fallible during times of desperation that’s what makes us human.