I understand that the main rationale for not publically disclosing the reason(s) for the decision to disfellowship an individual is based on strict legal advice to all bodies of elders (an announcement from the platform in the Kingdom Hall is by defintion a public announcement).
Potentially, an aggrieved party could sue the local body of elders for slander or breach of privacy, particularly if the circumstances surrounding the decision to disfellowship are in dispute (i.e., the individual denies allegations but others' testimony carries the day).
That said - ahem - the local kingdom hall gossip mill usually ensures that brothers and sisters have some idea about the reason(s) the individual was disfellowshipped. Years ago, within weeks of someone being disfellowshipped, there was invariably a local needs talk heavily alluding to the sin in question.