http://www.4jehovah.org/what-you-nee...ahs-witnesses/
Although that is a trinitarian site, the basic premise is correct: JWs at your doorstep are not there to discuss your beliefs, but to promote their organization.
I spent several months "studying" with a Pioneer and two Elders from the local Kingdom Hall. Believe, theological arguments are not what motivates them. Other than a newbie, a JW has a LOT invested in sticking with the Org.
Also, when they "do church" it is all about training in how to "witness" and deal with "objectors" who try to use Bible arguments.
You have to know how to plant seeds that they will ponder on their bed at night. You also HAVE to demonstrate and convince them that you are willing to be s genuine friend. They may come to you alone with questions, but if they get found out they suffer major repercussions. So if they don't REALLY trust you, you're not really going to get anywhere.
Newbies, though, haven't yet invested themselves so completely in the Org, so they still think in terms of "What does the Bible say?"
A cursory examination of Watchtower doctrines, and the changes they've made, is enough to convince just about anyone the Org isn't what it claims to be at all. Which raises the question, why do so many join and stay, even when shown the truth about the Org from its own publications? Well, it's because they aren't in it because they believe it's the truth. Rather, they believe it's the truth because they are in it.
And they are in it because it is all they have.