I don't have a reference at hand, but I seem to remember a remark in the Watchtower (or other JW literature), within the past 2 or 3 years, to the effect that if you haven't seen someone at the Kingdom Hall in a long time it's probably because they are living in 'serious sin.' (If someone has that reference, a note of it would be appreciated)
And how do JWs react to other JWs who are living in serious sin? They typically shun them, in this case even if there is no real indication of serious sin - Watchtower just planting the idea in the minds of JWs is enough.
Shunning has progressed over the years from JWs being completely against it (it was said to be unkind, unloving, unchristian, unscriptural, and a pagan practice), to only shunning DF'd people, to also shunning those who formally disassociate, to now shunning those who have quietly faded away.
In the case of many faders of course, they are not living in sin at all but have faded for solid reasons of conscience, but the Watchtower organization makes no allowances for conscience.
I believe this is a sign of desperation on Watchtower's part. It's about isolating JWs from anyone who might have an opposing point of view to a JW teaching.