Why did Charles de Gaulle resign as president in 1969?

Charles de Gaulle resigned as president of France in April 1969 following his defeat in a national referendum.12

Seeking to reaffirm his leadership after the social and political unrest of May 1968, de Gaulle proposed constitutional amendments regarding the regional reorganization of France and the reform of the Senate. He explicitly tied his political future to the outcome, announcing that he would resign if the measures were not approved by the electorate.12

On April 27, 1969, the referendum was defeated by a margin of 53 to 47 percent. True to his word, de Gaulle resigned the following day, effectively ending his political career and retiring to his country estate.21