Because JWs often prey on the uneducated and and "less intelligent" (sorry for the truth here) they don't have the capacity to truly "think" for themselves.
I feel like I have to correct this every time I see it. Jehovah's Witnesses are no less intelligent than anyone else. They are victims of mind control. Do some research on the methods cults use to indoctrinate people. Smart people fall for them all the time. They do not think for themselves, not because they lack the capacity, but becuase they have been trained not to.
I don't understand why people who have been part of the b0rg seem so surprised about lack of sustained friendships upon leaving. I thought the witnesses were very up front about this. They are friends only with other witnesses. It's in the charter. It's only surprising when a witness does maintain a friendship with someone who fades (my brother has a few good jw friends like this).