Why does civicrm_postProcess hook does not pass certain parameters?

Question

Only the "$formName" variable is getting supplied to the hook callback. Why are the rest of the variables listed in the documentation not getting supplied?

add_action('civicrm_postProcess', 'onFormSubmit');

function onFormSubmit() {
    $args = func_get_args(); // Returns ["CRM_Contribute_Form_Contribution"]
}

https://docs.civicrm.org/dev/en/latest/hooks/hook_civicrm_postProcess/

Answer 1

add_action defaults to 1 param: https://developer.wordpress.org/reference/functions/add_action/