I've been trying to implement a solution for setting taxonomy attributes on WooCommerce products. This is a the code I wrote:

$product = wc_get_product($product_id);

$taxonomy = 'pa_out-of-stock';
$false_term_name = 'false';
$true_term_name = 'true';

$false_term_id = get_term_by('name', $false_term_name, $taxonomy)->slug;
$true_term_id = get_term_by('name', $true_term_name, $taxonomy)->slug;

$attributes = (array) $product->get_attributes();

if (array_key_exists($taxonomy, $attributes)) {
    foreach (
        $attributes as $key => $attribute
    ) {
        if ($key == $taxonomy) {
            $options = $attribute->get_options();
            $options = array($true_term_id);
            $attribute->set_options($options);
            $attributes[$key] = $attribute;
            break;
        }
    }
    $product->set_attributes($attributes);
}
else {
    $attribute = new WC_Product_Attribute();

    $attribute->set_id(sizeof($attributes) + 1);
    $attribute->set_name($taxonomy);
    $attribute->set_options(array($false_term_id));
    $attribute->set_position(sizeof($attributes) + 1);
    $attribute->set_visible(true);
    $attribute->set_variation(false);
    $attributes[] = $attribute;

    $product->set_attributes($attributes);
}

$product->save();

I printed out the $product object and the set_options() function seems to be changing the value. But after the $product->save() function is called there seems to be no changes, the attribute term doesn't seem to change on the product. I checked the term ID's, they are correct. I checked the taxonomy slug, it also correct. The just seems that the saving is not working. Any ideas why this could be happening?