"Defamation essentially involves harm or injury to a person’s reputation.
"And reputation is a social concept: It refers to a person’s standing in some relevant audience, i.e., the group or community beyond the speaker and the person."
https://www.journaloffreespeechlaw.org/simons.pdf
On the above basis announcing a disfellowshipment could be considered defamatory. It is certainly going to harm a person's reputation within the JW circle.
Let's remember that the merest whiff of legal action will make the WT change policy.
https://www.jehovahs-witness.com/topic/8367/disassociation-versus-disfellowshipping
Defamation is mentioned in the above thread. From that thread:
"A couple of years ago, I asked an elder I knew well about this and other matters that had "wording" changed. Such as, not announcing why a person had been df'd. At the time, I was still active and didn't even know of the term 'disassociation.'
"His response? "Because they kept being sued, that's why! Satan is after the Society in any way he can. It's just words - they have to protect themselves."
"So....it's ok to change "words" to stay out of court. Such as disfellowshipped to disassociated. "It's just words" - the locals know that no real change has taken place"
It seems that the 2005 change relates to the above mentioned lawsuits.