I think it just boils down to people who are just plain "dumb". They think they KNOW how to drive, just because they have a licence and CAN drive, big difference.
"Hey let me get in my car and go to the shops, what's that?? A street sign?! I have no idea what it means. Oh look I'll just merge without looking too because I didn't really pay attention in driving school. Let's TRY and cause an accident today."
Depending on which popular city, the proportion of DUMB people increases.
There are also categories of stupid drivers, Mum's with missions in 4wDs, Asian women in camrys that takes 10 minutes to park in an open bay, Ute driving bogans who are aggressive, rude and careless. Not all of them are annoying and careless, but being a frequent driver, when you spot them, you'll just shake your head and say "typical".
There's probably no country/city with perfect drivers, I think in general Australians aren't prepared for stupid drivers, where in 3rd world countries "we" drive like mad anyway (yes I'm a halfie).
For the most part, Victorians are definately more polite in my experience, coming up from Sydney. But in defence, Sydney never used to be rude and careless too, I think these are all signs of big city syndrome, where no one gives a shit anymore.
Then the story continues with just general social and civic conciousness, but we'll leave that topic for another day. Just have to accept the fact of life that shit happens and live with it, if not "Go back to Spain"? Lol.