Elders are not trained in any field by the WTS, they are trained to follow the organization's views and teachings. They may be completely unprepared to deal with an issue that comes before them, because they frequently have no grounding in the ethical and practical considerations involved in these cases. Thus, they may take actions and make decisions that would shock anyone in a relevant field.
The WTS puts the lives and safety of people in the hands of men who are not prepared to deal with some of the issues they face, but are expected to do so while rejecting any outside help. And they are not obligated to recuse themselves, thus leading to decisions where a man is allowed to maintain a relationship with a teenager as long as he promises to marry her when she comes of age. Because I can't think of any other explanation for such a deranged decision.