Many fundamentalists are all anger when it comes to those who don't share their views. They like the fire and brimstone. JWs use shunning as the cold shoulder, passive aggressive equivalent. If they break you and force you to seek reinstatement, you are--in effect--saying, "I'm sorry. I was wrong. You are right."
It also allows them to feel superior. They stay the course like a good JW, and their glad they aren't like you.
In the end, it reinforces their self righteousness and keeps them away from those with new, independent ideas that could "corrupt" them. So it works on several levels. Just like field service. :-)
I doubt it's going anywhere.