What Up's With Gradpa?

When the Joads where first taking about going to California Grandpa was excited about going and wanted to squirt grapes all down his face. But when it was time to leave he did not want to leave and had to be druged to get on the truck. Later down the road Grandpa dies and the Joads say it is because he was taken away from his land and was heartbroken. If Grandpa was so upset about leaving his land that it caused him to die why did he want to leave it in the beginning? This did not make sense and if there was any symbolic meaning in his death I think this made the meaning unclear.