WordPress with WooCommerce extension by default hides categories which have no products inside. Unfortunately for some reasons there is no option in the backend of WooCommerce to change it. We need to add a simple snippet code to our functions.php file:

add_filter( 'woocommerce_product_subcategories_hide_empty', 'show_empty_categories', 10, 1 );
function show_empty_categories ( $show_empty ) {
   $show_empty  =  true;   
    return $show_empty;
}