I mean, one is already dead after hanging; everything else is just some extra burden on state finances. Your body will become dust anyway, quartered or not quartered.
Being hanged didn't make you dead. Not reliably. It's kind of a science; what happens when you drop depends on your weight, and the length of the drop. If you're too heavy, or the drop is too long, then your head gets yanked off, which is generally considered a bad result. On the other hand, if you're light or the drop is too short, you get slowly strangled, which is also an undesirable outcome.
So sometimes hangees would pay people to swing from their ankles after the drop, until they were really dead.
For hanging, drawing and quartering, you weren't supposed to die from the hanging bit.
[Edit] The quartering part wasn't some kind of superfluous state expense; it was the whole point of the exercise. HDQ was only performed rarely - it was reserved for the (commoner) leaders of rebellions against the monarch. Common criminals were just hanged.
