Putting nukes or tungsten rods in space wouldn't accomplish much. You can't just "drop" an object from orbit. Instead you need to conduct a burn to de-orbit and head toward the target. So it doesn't save much time compared to hitting the target directly with a missile launched from Earth. Launch satellites themselves would be vulnerable to anti-satellite defenses so they would be shot down early in any major conflict. And nuclear weapons can't be left unattended indefinitely; they require maintenance at least every few years in order to operate reliably.