Why is Tom Joad so reluctant to leave Oklahoma?

His family is gone. His home is destroyed. His friends are nowhere to be found. Even though there is nothing tangible to keep Tom Joad in his old neighborhood, he has one primary reason for his reluctance to leave Oklahoma: parole.
"Ever'body's goin' west," Tom said. "I got me a parole to keep. Can't leave the state."
Curious, Muley asks:
"How they treat ya there in McAlester? My woman's cousin was in McAlester an' they give him hell."
Tom replies:
"It ain't so bad," said Joad. "Like ever'place else. They give ya hell if ya raise hell."
McAlester prison opened in 1908 and was a relatively young facility when Tom Joad was admitted. Tom had been there four years, and was released three years early (“Sure I been in McAlester. Been there four years.” - Chapter 2; ). Based on these dates, it is likely that Tom Joad was incarcerated in McAlester from 1933-1937.
The doors locked behind Tom just as the storms were increasing in intensity. According to PBS’s “Timeline: Surviving the Dustbowl. 1931-1934,
“Great dust storms spread from the Dust Bowl area. The drought is the worst ever in U.S. history, covering more than 75 percent of the country and affecting 27 states severely.”
Before Tom went away, however, he was aware that some weather anomalies were occurring in Oklahoma. In 1932, PBS reports, fourteen significant dust storms had occurred. By 1933, that number had doubled.
The dust storms continued to occur, becoming even more frequent and powerful. On April 14, 1933, an horrific event known as the “Black Dustbowl” occurred, displacing some 300,000 tons of top soil and most greatly affecting the areas of Oklahoma and the Texas Panhandle. Then, in 1934, just one year after Tom went away, the “Yearbook of Agriculture” announced that,
Approximately 35 million acres of formerly cultivated land have essentially been destroyed for crop production…. 100 million acres now in crops have lost all or most of the topsoil; 125 million acres of land now in crops are rapidly losing topsoil.
When Tom is dropped off by the trucker, in 1937, what had been some abnormalities at home had become unmitigated disasters, and not all of them, of course, were weather-related. Banks were seizing farms by the hundreds, forcing their residents to go elsewhere. As the land was unusable, these displaced families had to go elsewhere.
The novel does not reveal how much, if any, of this was known to Tom prior to his release but his dismay indicates that he was ignorant of most of the events of the prior four years.
Tom’s world from 1933 to 1937 was necessarily interior although because of his assignment to a work crew, he could not have been completely in the dark about the dust storms. Tom, like thousands of others, was a participant in prison labor. Prisons had been in existence in America for about 100 years by the late 1930s and had remained largely unchanged: most were terrible and inmates were given only the bare necessities to survive. Privacy was not an option. What did change was the numbers of people, mostly men, who found themselves behind bars in by the late 1930s; incarceration rates climbed from 79 to 137 per 100,000 residents between 1925-1929.
Prison labor had long been a part of life for the incarcerated, who, unlike free citizens, could be compelled to work. While there were large numbers of black men and other minorities assigned to chain gangs and other work, the numbers of white men forced to work was relatively low in comparison. However, by 1934, many more white men were conscripted into service. The reason for this can be found in the growing numbers of inmates crammed in too-small housing. Riots were flaring more and more frequently and prison officials lobbied Congress to create a work program and in 1934, the 73rd Congress approved the Federal Prison Industries.
It was into this mix of circumstances that Tom Joad was thrown. It is likely that Tom worked on a road crew, as evidenced by the location of the callouses on his hands, which the trucker who lets Tom ride with him observes:
“I seen your hands. Been swingin' a pick or an ax or a sledge.”
Road crew workers often worked from sunup to sundown. Given the location of the work, sometimes cots were set up and the prisoners guarded while they slept so that they could be back on the job as soon as there was enough sunlight to do so.
No one would want to return to prison. But in 1937, for Tom Joad, violating his parole meant a return to subhuman conditions and a life of brutal work.
Sources:
http://www.pbs.org/wgbh/americanexperience/features/timeline/dustbowl/
http://www.michbar.org/journal/article.cfm?articleID=739&volumeID=58
Prisons: History - Modern Prisons - Incarceration, War, Imprisonment, and Prisoners - JRank Articleshttp://law.jrank.org/pages/1782/Prisons-History-Modern-prisons.html#ixzz3CY9Y1cDN