Maybe you are unaware of how media files work in WP.
As you can see in your code the files are posts with a post type of attachment
$attachments = get_posts( array(
'post_type' => 'attachment',
'posts_per_page' => -1,
'post_parent' => $post->ID,
'exclude' => get_post_thumbnail_id()
) );
every post that has a post type of attachment appears in the media library in WP. It would be impossible for you to display these files on the front of the site if they are deleted from the media library.
It is possible to hide files from appearing in the media library: https://www.google.com/search?q=hide+files+from+the+media+library+in+wp
https://wordpress.stackexchange.com/questions/271584/can-i-hide-the-attachments-from-media-which-i-uploaded-from-front-end
