I'm a born-in, third generation on both sides of my family.
I believe cold-call converts are in the minority nowadays. Non-JWs with JWs in their family background, or who were raised as such but never converted, seem susceptible. Above post mentioned being sucked in after being married to a JW or someone studying--that happens all too often to.
Apart from this, the cold-call converts, not born-in, no family--as someone mentioned, some change of life (sometimes tragic) leaves them open for a time in looking for answers and comfort. This is accompanied by love-bombing. As well as the convert does not INTEND to join anything...they are just having a "study" to learn more about the Bible with some nice people. And it is presented in a way that makes sense and seems consistent. JWs seem to have all the answers. Things progress slowly over months and years and by that time they are hooked.