I'm sure by now the GB has realized that preaching doesn't generate new converts; it never really did.
@redvip that is simply not true. Average anual population growth is now about 1%,.. during the sixties and during the last century it never was higher than about 2%
However the annual growth of JW's was much higher than the average population growth almost every single year. Bisides that many JW couples decide(d) not to take children because they place kingdom interests first or think that this system of things is not the right environment to raise children in,
In my congregations there are a lot of couples (pioneers en elders) that never got any children just because of that. So the birth rate among JW's is even less than the average birth rate in the world that surrounds them.
Conclusion: a lot of people came in through the preaching work. Even several members of the governing body are examples of that. take for example Gerrit Losch or Tony Morris III