The billionaire tears are so refreshing to drink from this article yes...quite a fine vintage.
I suspect the "reasons" are never going to be discussed; probably to prevent the same billionaires from money-ing their way out of this as well. Fortunately in countries like that; the Harbormaster's word IS LAW.
I suspect they simply don't want these sorts of luxury yachts clogging up the ports anyways and would rather that they anchor at a nearby port that is better equipped for them and use their smaller craft to visit Naples.
I could see how large yachts captained by assholes working for billionaires could be a safety hazard if they don't behave professionally or ethically in port or manage the expectations of an immature yacht owner.