For the last 20 years or so, most of the growth has been CHILDREN of JWS getting baptized. What keeps teenagers IN the Borg, is meeting other teenagers and eventually getting married and having children who get baptized in the Borg. With fewer and smaller conventions and opportunities to meet JWs of the opposite sex, I see more use of "unofficial" "JW" dating sites and dating non-JW workmates...thereby breaking the chain of generational JWs.
An "ex" JW friend regularly dates "JW" gals off JW dating sites. The gals don't care he is an ex-JW. He has the all books and can "talk the talk" to their families.
This is how the Shakers and Christian Scientists disappeared as religions.