I think conservative types are drawn to the witnesses for some reason. If one already feels that the "world" is too immoral, loose, depraved, wicked, violent, or just plain bad, then when they become a JW, it just intensifies that thinking and in the case of a lot of our parents causes them to become overly strict. Then they have the WTS to back them up for their prudish ways.
My parents, mother especially, were strict. I wasn't allowed to do things that even other JW kids were allowed to do. I endured it thinking that somehow my being different, 'persecuted' and living in a vacuum was making God happy and pleased with me, even though I was miserable. Now I realize that the JWs and the WTS were just enabling my mother to be an overly strict and prudish parent. She and her family have always been conservative and prudish types. By joining the JWs she was validated into thinking that becoming that overly strict parent was the right thing to do.
But I know not all JW parents were like that, I've met some good ones, who raised some good kids.