Why does the Joad family continue on this trip?

The Joads have one enormous factor in their favor, Ma never gives up. She is the backbone of the family, and she is determined to move forward and establish a better life for her children. It would have been easy to give up, and without Ma they probably would have, but she consistently doles out support, good advice, and most of all love...... she's a tough woman, and she lends that toughness to each member of the family.

One thinks that the joad family has no choice , if they return back home they will find nothing except the drought and greedy owner of the land so they must to cotinue in order to survive their life ; they have nothing except their unity which represents in Ma charachter