Final answer:
The California grape industry faced a boycott organized by Cesar Chavez and the United Farm Workers. the boycott targeted underpaid farm workers and urged consumers not to buy grapes or lettuce picked by them. this campaign had a significant impact on improving the conditions for the workers.
Step-by-step explanation:
The reason why many people weren't buying grapes at the grocery store was due to a boycott organized by Cesar Chavez and the United Farm Workers. The boycott aimed to raise awareness about the underpaid conditions of farm workers and to pressure California growers to improve these conditions. The campaign encouraged consumers not to buy grapes or lettuce picked by underpaid laborers. The boycott ultimately led to improvements for migrant laborers in the grape industry.