They do not
The undead are creatures, and are treated as such by the rules like any other creature. They simply have many exceptions and rules that interact specifically with their type of creature (undead or undead).
The resurrection can bring back someone who was turned undead and then destroyed, has no effect on the undead creatures in general. Unlike Raise Dead, which can not bring a creature that became undead and then was destroyed, the spell is simply not strong enough to fix the disaster that is not dead.
You can resurrect someone killed by a death effect or someone who has been become a dead creature and then destroyed. You can not resuscitate someone who has died of old age. Construct, elementals, outsiders, and Undead creatures can not be resurrected.