Well aside from keynesian economics not actually being an HSC topic in itself you probably dont need to waste your time on it.
But heres my thoughts.
The HSC course is an outdated, and left wing economics course. Basically everything you learn in it comes from a keynesian perspective.
John Maynard Keynes wrote a very influention publication in the 1930's entitled "the general theory of employment, interest and money". This piece of work basically attempted to answer what policy makers "should" have done in order to prevent the great depression.
What he came up with was a notion of contractionary and expansionary macroeconomic policies that should be used to smooth out the economic cycle. At this time, there was a belief in the "demand" side of the economy, and that all the troubles within the economy were from a "demand" perspective.
Governments largely adopted his economic policies, until the 1970's where this thing called "stagflation" (high unemployment and inflation) occured. Policy makers started to look at their policies, and gradually a few trends emerged:
1 - Policy makers started to think of the underlying problems in an economy as being more of a supply issue rather than a demand issue (so thats why microeconomic reform was a big thing from the 1970's onwards)
2 - Policy makers started to question the effectiveness of macroeconomic policies in solving economic problems. A recession could not be solved by simply reducing interest rates, or running budget deficits, as there were profound consequences of doing so.
3 - A new way of thinking came to surface. Known as "monetarism", it was championed by the famous economist "Milton Friedman" and his mates (who have become known as the "chicago school"). Monetarism essentially suggested that the money supply was largely responsible for inflation.
4 - A new wave of policitical thinking swept the world. Margaret thatcher took to 10 downing street with her liberalist market (free markets) policies (policies usually branded as thatcherism). Ronald reagan moved into the white house and essentially applied the same policies (with his policies refered to as reagonomics). Essentially these leaders refuted Keynesian economics, and adopted many of Friedmans suggestions.
So to cut a long story short, keynesianism is fundamentally flawed, meaning that just about the whole basis of your HSC studies is incorrect. There are still predominant left wing interests still promoting keynesianism, howevor the reality of the situation is that very few economists would swear by keynesianism anymore. Whether that means we should be teaching neo classical economics, or monetarism, or whatever is not being disputed, but the fact is that to have an HSC course not even allude to these other ways of thinking yet be grounded in such an outdated framework is somewhat absurd.
The only real reason I can think of is that most teachers dont know anything apart from what they've been teaching for the last 30 years, so they dont want to change it. A fairly backward way of thinking.....