I can’t access custom taxonomy page listing

The only problem that I have found is 'query_var' => 'news' in register_taxonomy(). Change it to 'query_var' => true and it will start working.

function create_my_taxonomies() {
        register_taxonomy(
            'news_categories',
            'news',
            array(
                'labels' => array(
                    'name' => 'News Categories',
                    'add_new_item' => 'Add New Category',
                    'new_item_name' => "New Category"
                ),
                'query_var' => true,
                'show_ui' => true,
                'show_tagcloud' => false,
                'hierarchical' => true,
                'rewrite' => array(
                    'slug' => 'news'
                )
            )
        );
    }

Reference: Codex Register Taxonomy