I've been following the decline of religion for quite a while now.
This is about JW's:
Jehovah’s Witnesses have the lowest retention rate relative to any other U.S. religious group. Among all U.S. adults who were raised as Jehovah’s Witnesses, two-thirds (66%) no longer identify with the group.
My personal experience with the group agrees with this - nearly all the kids my kids grew up with - have left the group or are only there because they don't want to lose their families. I believe the retention rate would be much, much lower if they eliminated the shunning policy. It's reflected in my own family - Out of myself and 4 other siblings, only 2 are PIMI, the rest of us are POMO. Out of 8 grandchildren, only 3 are PIMI, 2 are PIMO and the rest are POMO.