You could always go in to work on a day off for a briefing, as you expect your Union Reps to do. How many briefing are they expected to give? How much of their spare time are they expected to give up? And you can't be bothered to give up an hour or two of your own time.
Just plain lazy!
I didn't go either. First one on a day off, then two more on leave and then yesterdays one finished before i went to work. Oh and i didn't get told about them until i went to work. Four briefings in four days aren't enough to get everyone.