How do the novels serve as a vehicle for social change? (The Pearl and Of Mice and Men)

Both The Pearl and Of Mice and Men show how the people at the bottom of the social and economic ladder are crushed by the forces that conspire against them. In both novellas, characters face societies that value money more than human beings. By painting sympathetic portraits of the struggles and the suffering of people at the lowest end of the economic strata, Steinbeck critiques the existing social order, hoping to inspire people to change society so that it is not so harsh towards those without.
Two examples of society valuing money over people in The Pearl are as follows: when Juana and Kino's baby, Coyotito, is stung by a scorpion, the local doctor refuses to treat the baby because Kino cannot afford to pay--but after Kino finds the pearl, the doctor insists on treating the baby. Second, the pearl dealers in La Paz work together to cheat the natives of a fair price for the pearls they find. Although Kino's pearl is worth 50,000 pesos, the dealers will only offer him 1,000 pesos.
In Of Mice and Men, the seasonal migrant ranch hands are paid as little as possible and have to share a rough bunk house with few amenities. There is no job security, and the men have a difficult time saving money. Although Lennie and George have a dream of owning their own farm, when George has to kill Lennie, that dream dies. Likewise, the dreams Kino had after finding the pearl die.
Steinbeck wants his readers to see that a kinder world that valued people more instead of grinding every last bit of money and hope out of them would be a better place to live. He wants to show how difficult, if not impossible, it is for people to climb out of poverty. This, he hoped, would make others more likely to want to feel the pain of the poor and want to build a society built on mutual care that gives people a helping hand.
Steinbeck himself was associated with communists in the 1930s. Because of his political orientation, he wanted to shine a light on how the simplest people suffered. Since he wrote his novellas decades ago, more of a safety net has been put into place to help those at the bottom, and perhaps to some small extent Steinbeck's work contributed to that.