That is the (in-game) reason why "Raise Dead" have a time limit of a few days before it no longer works. After some time, the soul you are trying to push back simply don't remember being alive, and do not wish to leave Dolurrh. More powerful divine casters can still bring souls back (Ressurrection), but is a considerably harder task.
Obviously, this affects the way some religious philosophies see the world. Silver Flamers believe that the most righteous souls join the Flame instead of going to Dolurrh. Blood of Vol believes that once your soul goes to Dolurrh, you lose your "inner divinity", and is no longer able to seek divinity on your own. The most numerous faith of the Host just believe "this is what the Host decided, and is how it shall be".
Intelligent undeads (wights, ghosts, wraiths, vampires, mummies...) don't have a soul. They have evil power with a glimpse of their former personalities guiding their bodies. Liches are the exception, because they lock their souls in their philacteries while they are still alive.