The Government doesn't tax imported vehicles "stupidly". They cop all the same taxes as a locally made car + 5% import tariff which is, by world standards, very, very low. China tariffs can be up to 40% depending on car make and type. I'm not 100% sure what the US tariff rate is, but I think it's somewhere around 25%. I could be wrong on this, however.
What you need to realise is that the car manufacturer employ hundreds of thousands of people in Australia both directly and indirectly. Every other country with a car industry provides massive funding to their industry meaning if we want auto manufacturing, we have to do the same or else our cars will become far more expensive in comparison and no one will by them.
If we were to withdraw support for car making, the economic ramifications would be far greater than the money saved invested elsewhere. To get out of car making we have to do it gradually, if at all.
If other governments were to reduce or remove their funding of their auto industries, their cars would become far, far more expensive and would not be able to compete with locally made cars on a value basis.
Giving money to auto manufacturers is a catch 22. Damned if you do, damned if you don't and at this stage the damning for doing is greater than the damning for don'ting.