Something that may explain that is that many of us tend to forget an important thing. The WT and other cults teach many things about what/how people must live their lives. But that's only one part of what they do.
In order for these controlling groups to maintain control over their people, they also give messages about how horrible their lives will be if they leave, and how horrible life is outside of their place. The brainwashing is not only about what they should do and be when they are in, but also about how terrible and empty their lives are supposed to become out there in "the world".
Look at how many ridiculous things they say about the world outside, and how everything that happens in the world is supposed to be bad, not worthy or deserving of destruction.
When a person leaves, that's what they fear they will be facing, and if they don't know how to deal with being made believe that the world out there is horrible, the very moment when something challenging happens to them, they may feel that the nonsense they were taught was right.
Some people don't have the emotional strength to deal with life challenges. That's why some join the JWs in the first place. So the moment they have a bad experience, I can see how the WT will look attractive to them.
That goes beyond people's sexual orientation.