Why did efforts to organize farmworkers fail prior to the leadership of Cesar Chavez?
Cesar Chavez, besides being very likable, charismatic and intelligent, was also more successful in his organizing efforts because of the timing of the United Farm Workers movement, taking place in the protest 60s, at the same time as other non-violent protests, particularly for civil rights, were gaining popularity, social acceptance and political success.
Chavez also recognized the effectiveness of two key elements of protest: boycott and non-violence. He organized a nationwide boycott of grapes (as oppsoed to previous local efforts that largely failed to gain public attention or support), went on a hunger strike and convinced his contemporaries in the movement to practice non-violence.
The demographics for Latinos, in California especially, also favored the timing of his movement. The number of recent immigrants as well as long term Chicano families was rising in the 1960s, giving them more voting power, more economic power and more public recognition. All of these in combination made Chavez more successful than efforts before him.