The award itself has a list of respondents at the back.
People not on the list do not necessarily pay less than the award. Many have their own workplace agreements based on the award, but better and more apropriate than the award for their organisations. The award has some crazy elements eg the casual instructor who comes in for a half hour TIF has to be paid for four hours work. Flying schools simply can't afford that. The whole point of employing casuals is that they are a variable, not an overhead cost, and that is what their 25% loading is for. So where is the money for the other 3 1/2 hours going to come from?
If the award was more reasonable in things like this maybe more people would pay it.
And yes elements in AOPA seem to think that instructors wages are one of these "unnecessary costs" that they dislike so much. Wicked, greedy instructors who want to earn a living should be stamped out so that PPLs can do it for the love of it, apparently, this is well covered in other threads.