Why are some of my custom posts not showing up on my page?

If you don’t set a value for posts_per_page, it will use whatever the setting is for Blog pages show at most under Settings > Reading.

Also, don’t use query_posts, use WP_Query instead:

$args = array(
    'post_type' => 'cases',
    'posts_per_page' => -1 // get all cases
);
$cases = new WP_Query( $args );
if ( $cases->have_posts() ) :
    while ( $cases->have_posts() ) :
        $cases->the_post();
        // output case
    endwhile;
else:
    // nothing found
endif;