There is no requirement to make the PA. Individuals (read Captains) may choose to make the PA or not. They CANNOT be forced to do so by the union and no FO or SO is going to make the PA without the Captain's say so.
Remember, only 83% total of the eligible pilots voted for PIA. While that is an overwhelming majority, the 17% who didn't probably incorporate some of the most senior captains on the retirement bus.
They may choose to make the PA or not. Fair enough, that's their choice. For example, I reckon it's a pretty fair bet that the PA wasn't made on Friday night's QF30!
