Product Post Editor

Currently it’s by design that products are edited using the classic editor. There are plans to switch to the Blocks editor in the future.

Interesting read: https://woocommerce.com/posts/woocommerce-and-wordpress-5-0/

FYI: This is the snippet in WooCommerce that disabled the block editor for products (includes/class-wc-post-types.php):

    /**
     * Disable Gutenberg for products.
     *
     * @param bool   $can_edit Whether the post type can be edited or not.
     * @param string $post_type The post type being checked.
     * @return bool
     */
    public static function gutenberg_can_edit_post_type( $can_edit, $post_type ) {
        return 'product' === $post_type ? false : $can_edit;
    }