Just last week we were vectored all over the sky with just two a/c (us and another) on approach, for no reason whatsoever. It was a gin clear night, so we could see there weren't any other a/c to affect.
Sometimes there is stuff happening on the ground that MIGHT (don't know if this was the case of course) occasion aircraft being vectored about the sky on a gin clear night. Aircrew don't ALWAYS have the full picture.