Default Autoship by default instead of one-time purchase

functions.php

// Default the Autoship option for both Simple and
// Variable products by default.
function xx_default_autoship_for_all( $default ){
  return 'yes';
}
add_filter('autoship_default_product_schedule_options_choice_value', 'xx_default_autoship_for_all', 10 ,1);

Important Notes:

• always test on a staging or development site first before publishing to your production site
• this code snippet should be added to the functions.php file in your active theme (or child theme)
• the "xx" value makes the name of the function unique. You can use it as-is (xx) or replace it.