Only recently has Australia expanded greatly into using the $2 coin for commemoratives. For many years after the first circulating $2 coin was issued, it was the current (and standard) obverse and reverse designs.
I think it's quite obvious why the $2 coin has been used so much lately: Seigniorage. Probably the most profitable circulation coin for the RAM.
The $2 cc that have been issued were mostly coloured and thus mostly taken out of circulation.
I also think that the RAM should slow down issuing $2 cc a bit. Wishful thinking on my part, of course. Not going to happen.
In 2018, we can most likely expect three coloured $2 commemorating the Commenwealth Games.