If they state a specific reason (eg theft) when the person hasn't been found guilty in a criminal court of law, they face liability for slander (and are less able to defend against such a suit, as the best defense against slander is truth, and a criminal conviction for the act serves as proof). Elders are not criminal investigators and face liability for stating someone committed a crime (or act, eg adultery) when it hasn't been proven in a court of law.
It's similar to the principle from employment law: if the employment terms were "at-will" and the employer needs to fire the employee, it's smarter if the employer doesn't give a specific reason for terminating them, just to avoid a wrongful discharge suit. After all, that's the WHOLE POINT of the at-will arrangement: either side can terminate the relationship at their will, but any reason offered can only potentially be used against them to support a claim.
But practically speaking, for most R&F members, the difference between DF vs DA is pedantic, creating a distinction without a difference: the end effects are the same.