It's definitely not the fact that the workforce is unionised...
Probably the fact lately that most of their crews have been screwed sideways by management has morale low with the roll on effect of lowered service standards.
I have flown Qantas a few times and have never had a bad customer service experience from them, even at the tail end of long haul flights where everyone is ready to finish up.
Perhaps you should look at your attitude and just see if it is being mirrored back at you...