get_post_field unexpected results

I am trying to use get_post_field to get the menu_order of posts.
My code looks like

$order = get_post_field($id,'menu_order','raw');

When I do a var_dump on $order, I get an empty string.

When I change my code to:
$order = get_post($id)->menu_order;

A var_dump of $order results in an int with the correct menu_order from the db. Why the difference? I even looked at the get_post_field function; it appears to be a wrapper for what my second code set does.