使用Wordpress WP_Filesystem_Direct和PSR-4自动加载

Question

I am utilizing composer w/ PSR-4 autoloading in a Wordpress plugin. No probs.

I went to use the WP_Filesystem_Direct class to remove a directory in a certain circumstance, but I found that I HAD to include 3 Wordpress classes manually using require in order to get things to work as expected.

Can anyone explain why I had to require them, and simply using them wouldn't work?

The following is the code that worked:

namespace Cre\API;

use \WP_Filesystem_Direct;

class ThingSync extends Sync
{
    public function checkPostProcessTasks()
    {
        // Why do I need this, and 'using' them above the class won't work?
        require_once(ABSPATH . '/wp-admin/includes/class-wp-filesystem-base.php');
        require_once(ABSPATH . '/wp-admin/includes/class-wp-filesystem-direct.php');
        require_once(ABSPATH . '/wp-includes/class-wp-error.php');

        if (get_option('deleteDir') !== "on") {
            $fs = new WP_Filesystem_Direct(false);
            $fs->rmdir(IMAGE_PATH, true);
        }
    }
}