^^^^
Having a big spectacle of your execution occur and then walking around in the same town the next day is jarring to those involved, and makes little in the way of any sort of RP development within the world. Many consider their characters irreplaceable and would not think of permanently killing them, this can be a selfish line of thought with you depriving many of what could potentially be rather impacting RP.
The assassination of King Franz and many of those with him at the time is the perfect example of what can be achieved through the permanent killing of your character, as the act of betrayal that occurred with that event would not be nearly as enjoyable had those involved chose to not PK their characters.