Why won’t my posts sort by post_name (slug)?

Here’s my code:
<?php get_posts('orderby=post_name&order=DESC'); ?>
<ul class="menubox"><?php while (have_posts('')) : the_post(''); ?>

<li><a href="<?php the_permalink() ?>"><?php the_excerpt(); ?><?php the_title(); ?></a></li>
<?php endwhile; ?>
</ul>

and here’s my URL: https://tinyurl.com/lof3u (please don’t post the actual URL, I don’t want the thread to cache on google)

What am I doing wrong? I made the post slugs just the last names so that I could sort the page alphabetically… and I can’t figure out how to make it happen.