It sounds like you are expecting people to behave rationally. Some people do quite well at that, but a lot don't. I'm in a somewhat similar situation - my never-been-a-JW father-in-law is studying with the JWs and progressing towards baptism, even after I gave him a book (that I wrote) spilling the beans on TTATT, and doing his own research online. My brother, who has previously commented that it is a cult, is quite bitter about the way he was harshly disciplined as a child by our JW parents, and is very well aware that the religion makes no sense is also now studying with JWs. My ex sister-in-law vacillates between believing it and not believing it, and again, I have spilled the beans with her. My wife knows enough to know that it is not true, but she still believes.
What all these people have in common is that they are not critical thinkers, and are instead reacting to needs and desires that are being fulfilled by what the JWs have to offer. A sense of community, a way to avoid confronting ones own mortality, a purpose in life, instant friends, an authority to tell them what to think and do. Whether it is true or not is not especially relevant - what is "true" today might not be "true" tomorrow anyway. It is sad, and frustrating, but I don't think there is much we can do about it. You can't force someone to think critically.