Shunning is a fundamental necessity for cults. It's part of the information control. Brand outsiders as "of the Devil", brand outside information as "of the Devil", brand ex-members as "demonic", brand every other religion as "demonic".
Every major issue of the Society for the last several years has been about controlling information. The Internet has been demonized, higher education has been demonized, promotion of the "faithful and discreet slave" has been pounded relentlessly. Many of the long-standing rules - reading "apostate" materials, talking to ex-members, accepting religious literature, reading the Bible without Watchtower input, examining the history of the Society, researching correct translation of Koine and Hebrew verses, etc. - are all about information control.
Any cult that is going to flourish needs to keep its members ignorant and defensive. Once non-members of the cult are perceived as "the enemy", the cult members herd themselves. 7M people around the world can't be controlled by some old geezers in NY. So, you give special titles to some of the more hard-core cult members who are good and brainwashed -e.g. "elder", "circuit overseer" - and tell the peons those guys are hand-picked by God.
Delegating authority doesn't reduce the centralized power, but multiplies it and spreads it wider. The elders are the eyes and fists of the Governing Body, but are perceived as representatives of God. Without their "God" mask, these construction workers in polyester suits wouldn't get any respect at all.