List product variations using wc_dropdown_variation_attribute_options in Woocommerce

The code that you have there comes from single-product/add-to-cart/variable.php template.

But you can't use it with $product->get_attributes() in the foreach loop.

In this template, $attributes is $product->get_variation_attributes()…

So the following code will work to display the attributes dropdowns (where $product is an instance of the variable product object):

<?php$attributes = $product->get_variation_attributes();$attribute_keys = array_keys( $attributes );?><?php foreach ( $attributes as $attribute_name => $options ) : ?>    <tr>        <td class="label"><label for="<?php echo sanitize_title( $attribute_name ); ?>"><?php echo wc_attribute_label( $attribute_name ); ?></label></td>        <td class="value">            <?php                $selected = isset( $_REQUEST[ 'attribute_' . sanitize_title( $attribute_name ) ] ) ? wc_clean( urldecode( $_REQUEST[ 'attribute_' . sanitize_title( $attribute_name ) ] ) ) : $product->get_variation_default_attribute( $attribute_name );                $args = array( 'options' => $options, 'attribute' => $attribute_name, 'product' => $product, 'selected' => $selected );                wc_dropdown_variation_attribute_options( $args );                echo end( $attribute_keys ) === $attribute_name ? apply_filters( 'woocommerce_reset_variations_link', '<a class="reset_variations" href="#">' . __( 'Clear', 'woocommerce' ) . '</a>' ) : '';            ?>        </td>    </tr><?php endforeach; ?>

As you can see the wc_dropdown_variation_attribute_options() function is made to display variation attribute dropdowns for the current variable product, BUT NOT a list of variations in a drop down.

List in a dropdown the product variations of a variable product:

To list all variation attributes in a dropdown you will use the following code (where $product is an instance of the variable product object):

$available_variations = $product->get_available_variations();if( count($available_variations) > 0 ){    $output = '<div class="product-variations-dropdown">        <select id="available-variations" class="" name="available_variations">';    $output .= '<option value="">'. __('Choose a variation') .'</option>';    foreach( $available_variations as $variation ){        $option_value = array();        foreach( $variation['attributes'] as $attribute => $term_slug ){            $taxonomy = str_replace( 'attribute_', '', $attribute );            $attribute_name = get_taxonomy( $taxonomy )->labels->singular_name; // Attribute name            $term_name = get_term_by( 'slug', $term_slug, $taxonomy )->name; // Attribute value term name            $option_value[] = $attribute_name . ': '.$term_name;        }        $option_value = implode( ' | ', $option_value );        $output .= '<option value="'.$variation['variation_id'].'">'.$option_value.'</option>';    }    $output .= '        </select>    </div>';    echo $output;}

Code is tested and works

To get an instance of the variable product object from a defined $product_id (where $product_id is the ID of a variable product) you will use:

$product = wc_get_product($product_id);