Criar diretório multinível

Uma pergunta, porque o script criar o diretório para esse caminho:

$targetDir = '../../img/anuncios/'.$id_user.'/';

e não cria para esse ?

$targetDir = '../../img/anuncios/'.$id_user.'/'.$id_anuncio.'/';

A classe upload.php

<?php
 include_once '../config/config.php';

/**
* upload.php
*
* Copyright 2013, Moxiecode Systems AB
* Released under GPL License.
*
* License: http://www.plupload.com/license
* Contributing: http://www.plupload.com/contributing
*/

#!! IMPORTANT:
#!! this file is just an example, it doesn't incorporate any security checks and
#!! is not recommended to be used in production environment as it is. Be sure to
#!! revise it and customize to your needs.

// Make sure file is not cached (as it happens for example on iOS devices)

header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
header("Cache-Control: no-store, no-cache, must-revalidate");
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");

/*
// Support CORS
header("Access-Control-Allow-Origin: *");
// other CORS headers if any...
if ($_SERVER['REQUEST_METHOD'] == 'OPTIONS') {
exit; // finish preflight CORS requests here
}
*/

// 5 minutes execution time
@set_time_limit(5 * 60);

// Uncomment this one to fake upload time
// usleep(5000);

// Settings

//$targetDir = ini_get("upload_tmp_dir") . DIRECTORY_SEPARATOR . "plupload";

$sql_last_ads = "SELECT * FROM table ORDER BY id_anuncio DESC LIMIT 1;";
$run_last_ads = mysql_query($sql_last_ads);
$row_last_ads = @mysql_num_rows($run_last_ads);

if($row_last_ads > 0)

{

$linha_last_ads = mysql_fetch_object($run_last_ads);
$id_anuncio = $linha_last_ads->id_anuncio;
$id_user = $linha_last_ads->id_user;
}

$targetDir = '../../img/anuncios/'.$id_user.'/'.$id_anuncio.'/';

$cleanupTargetDir = true; // Remove old files
$maxFileAge = 5 * 3600; // Temp file age in seconds

// Create target dir
if (!file_exists($targetDir)) {

@mkdir($targetDir);
}

// Get a file name

if (isset($_REQUEST["name"])) {
$fileName = $_REQUEST["name"];
} elseif (!empty($_FILES)) {
$fileName = $_FILES["file"]["name"];

} else {

$fileName = uniqid("file_");
}

$filePath = $targetDir . DIRECTORY_SEPARATOR . $fileName;

// Chunking might be enabled

$chunk = isset($_REQUEST["chunk"]) ? intval($_REQUEST["chunk"]) : 0;
$chunks = isset($_REQUEST["chunks"]) ? intval($_REQUEST["chunks"]) : 0;

// Remove old temp files
if ($cleanupTargetDir) {
if (!is_dir($targetDir) || !$dir = opendir($targetDir)) {

die('{"jsonrpc" : "2.0", "error" : {"code": 100, "message": "Failed to open temp directory."}, "id" : "id"}');
}

while (($file = readdir($dir)) !== false) {
$tmpfilePath = $targetDir . DIRECTORY_SEPARATOR . $file;

// Save the image on bd
if($tmpfilePath == true)
{

// If temp file is current file proceed to the next

if ($tmpfilePath == "{$filePath}.part") {
continue;
}

// Remove temp file if it is older than the max age and is not the current file
if (preg_match('/\.part$/', $file) && (filemtime($tmpfilePath) < time() - $maxFileAge)) {

@unlink($tmpfilePath);
}
}
closedir($dir);
}

// Open temp file
if (!$out = @fopen("{$filePath}.part", $chunks ? "ab" : "wb")) {

die('{"jsonrpc" : "2.0", "error" : {"code": 102, "message": "Failed to open output stream."}, "id" : "id"}');
}

if (!empty($_FILES)) {
if ($_FILES["file"]["error"] || !is_uploaded_file($_FILES["file"]["tmp_name"])) {
die('{"jsonrpc" : "2.0", "error" : {"code": 103, "message": "Failed to move uploaded file."}, "id" : "id"}');
}

// Read binary input stream and append it to temp file

if (!$in = @fopen($_FILES["file"]["tmp_name"], "rb")) {
die('{"jsonrpc" : "2.0", "error" : {"code": 101, "message": "Failed to open input stream."}, "id" : "id"}');
}

} else {
if (!$in = @fopen("php://input", "rb")) {

die('{"jsonrpc" : "2.0", "error" : {"code": 101, "message": "Failed to open input stream."}, "id" : "id"}');
}
}

while ($buff = fread($in, 4096)) {

fwrite($out, $buff);
}

@fclose($out);
@fclose($in);

// Check if file has been uploaded
if (!$chunks || $chunk == $chunks - 1) {
// Strip the temp .part suffix off

rename("{$filePath}.part", $filePath);
}

// Return Success JSON-RPC response
die('{"jsonrpc" : "2.0", "result" : null, "id" : "id"}');