This was such a weird move across the board. Climate change rejection aside though, I think there could be a sympathetic (to the government) explanation somewhere in there:

Eventually, EVs will need to be taxed in some way, if only to make up for the loss of fuel excise tax. It's far less controversial (and politically suicidal) to introduce a tax when only a tiny percentage of (presumably non-politically-donating) Australians will actually have to pay it.

Then once EV usage hits a significant percentage, there's already a tax in place that everyone takes for granted. And in the very unlikely event that such a tax would be repealed, what a great card to play at election time.

I can't remember who said it, but it reminds me of the "we should have taxed the Internet when we had the chance" comment. A realisation which came far too late (thankfully) for the government to do anything about it.