The writing of the migrant farmers held a great deal of allure to Steinbeck because their predicament was so opposite of what American identity was comprised. When one thinks of American Identity, the immediate connotations that enter one's mind are the notion of economic success, roots in a home, the development of a happy family, and a general sense of contentment in one's setting and the world in which one is enveloped. However, in writing about the migrant worker in the 1930s, this state of reality is entirely contrasted with the predicament that faced the migrant farmer. Struggling for work, they moved from place to place without a clear sense of home in an almost rootless existence driven to find work and a means of subsistence. As America grows into greater awareness of self, Steinbeck's writing of the migrant farmer helped to drive home the idea that the concept of "America" has to encompass more voices, more experiences, and the narratives that might run counter to what individuals might consider the positive and upside of "American Identity." Steinbeck's writing of the migrant worker is an absolute reminder that for all of the successes of America, the plight of the migrant worker or farmer is one that has to be acknowledged and validated as a part of "America."
A prevalent theme with John Steinbeck is the alienation of people during the Great Depression. A socialist, Steinbeck promulgated his message of the brotherhood of man as the answer to this disenfranchisement and alienation that people suffered in the desperate 1930s when families were separated and men were forced to migrate to areas where they could find work. Steinbeck's great novel, "The Grapes of Wrath," which he wrote one year after "Of Mice and Men," has the same theme of the brotherhood of man as his novella. With his writings and activism, Steinbeck hoped to bring attention to the plight of the Oakies in "Grapes of Wrath" and the migrant workers in general , a group in "Of Mice and Men." These lonely, desperate men were ones with whom Steinbeck had worked and with whom he sympathized.
Steinbeck worked throughout his summers in the early 20s as a farmhand and rancher in the Salinas Valley area. Although the 20s preceded the 30s Depression era that he wrote about, chances are, he well understood the plight of young men working for a period of time to just make a few bucks while there were bucks to be made despite the purpose.
He actually attended Salinas High School, so he well knew the area. As his writing career was taking off and his worldview was taking shape, the Depression hit. Obviously his writing demonstrates sensitivity to the Depression. Born in 1902, he was in his 30s then. This time period for most is a securing of identity and understanding of the world around us.
There is a national society devoted to maintaining his legend. Check out steinbeck.org
Steinbeck writes about people like this because he was writing during the Great Depression. During the Depression there were a lot of people who were wandering around, looking for work. Many of them came to California, like George and Lennie did and like the characters in "The Grapes of Wrath" do.
Because Steinbeck was from that area of California (the Central Valley where this novella is set), he saw quite a few of these people and felt sympathy for their plight. He felt that they were people whose lives had been devastated by the economic system of that time. That is why he wrote about them.
Migrant farmers of the time, the Depression-era 1930's were the perfect examples of people falling through the cracks of society. Those who had no job security, moved from place to place in search of temporary work, and came from all segments of society - the elderly, the mentally challenged, the poor, the uneducated - all are represented in the story so the reader can get a good look at what all of society was experiencing during that time. In other words, he wrote about migrant farmers because they were representative of America.
Steinbeck also wrote what he knew, since he grew up and lived in agricultural California.