Deathrattle Skeletons are the inheritance of the barrow-kingdoms: whole armies of ancient soldiery called back to the colors centuries after the colors rotted away. They advance in disciplined ranks, spears levelled with the muscle-memory of drills practiced in life, shields locking out of habit rather than fear. They feel nothing, tire of nothing, and stop for nothing short of the will that binds them.
It is the oath, not the flesh, that necromancy summons back to service. Wight-lords still command companies they led a thousand years ago, and standard bearers still carry the devices of nations no living scholar can name. Cut one down and the bones simply gather themselves and resume their place in line — the soldiers of the old kingdoms gave their lives long ago, and see no reason to give ground as well.