Make order status completed when an order is placed - WebToffee WooCommerce Subscriptions

functions.php

add_action( 'woocommerce_order_status_processing', 'processing_to_completed');

function processing_to_completed($order_id){

    $order = new WC_Order($order_id);
    $order->update_status('completed'); 

}

Do you know why WooCommerce Subscriptions do not automatically set the order as Completed when the card has been charged? I mean, it's a virtual product so it should be made Completed. Since it's an official plugin by Automattic, I find it strange that they've chosen to neglect this obvious flaw. That is, unless I'm missing something.