I am just wondering if part of the appeal of planning is that you get to "leave your mark" on the world? It would seem that there aren't many jobs where you get to do this, as usually one is creating a product of some sort that will eventually be outdated. With planning, though, you can very realistically do something that changes the face of the city, then drive around 20-years later and say, "See that? I was responsible for making it look that way."
I don't know if this is entirely realistic but I imagine that there are plenty of similar examples. It seems that this would be one of the largest sources of job satisfaction... for me anyway.