Why didn't George leave the ranch with Lennie when he said they were going to have trouble there?

George and Lennie were flat broke. They had traveled hundreds of miles from the town of Weed in northwestern California to "a few miles south of Soledad," a small farming town about 25 miles south of the much larger town of Salinas, which is situated about 100 miles south of San Francisco. They had picked up work tickets at a hiring hall for unskilled laborers in San Francisco and badly needed the jobs at the ranch they were headed for when the novel opens.

At their riverside campsite they had eaten their last three cans of beans. If they didn't get the jobs and hold on to them for at least a month until they each received their fifty-dollar monthly wages, they would be truly desperate. The fact that George was anticipating trouble did not mean he thought they should leave. He was used to trouble, and he knew they might have worse trouble if they went back on the road with no money and no food. 

John Steinbeck has George warn Lennie to expect trouble as a form of foreshadowing. These two men have had troubles in the past, but their worst troubles lurk ahead.