By default, users don't have excerpts displayed in the admin...this forces it.

force-page-excerpt-into-admin.php

// Force Page CPT to have excerpt (all users)
// -------------------------------------------------------------
if ( is_admin() ) :
  function force_excerpt_box() {

    // get all post types (excluding posts)
    $post_types = array('page');

    // get all users
    $all_users = get_users( );
    $user_list = array();

    $hide_boxes = array(
        'postcustom',
        'trackbacksdiv',
        'commentstatusdiv',
        'commentsdiv',
        'slugdiv',
        'authordiv',
        'revisionsdiv',
    );

    foreach($all_users as $user):
      $user_list[] = $user->id;
    endforeach;

    foreach($user_list as $user):

      foreach($post_types as $post_type):
        update_user_option($user, 'metaboxhidden_'.$post_type, $hide_boxes);
      endforeach;

    endforeach;

    update_user_option(1, 'metaboxhidden_page', $hide);

  }
  add_action( 'admin_menu', 'force_excerpt_box' );
endif;

New users are created with certain admin settings pre-set...this includes not seeing the Page's excerpt in the admin. This forces all users to have certain box settings hidden, excluding the excerpt.