A few thoughts.
1. The media has a large part to play in this, demonising and dehumanising cyclists, so that some drivers actually do believe cyclists are not allowed on the road. The unmoderated commenting on news sites and social media makes that message even worse. Some of the bile, viciousness, callousness and genuine hate in those comments is truly frightening. Even on VicRoads' or VicPol's sites where there's a cycling law explained or a cycling incident, some of the comments are disgusting and just let go without any action taken on them. It's no surprise that some drivers see cyclists as inconsequential or even fair game.
2. Every driver knows you must stop if you have a collision. Even if a road user "shouldn't be there", such as a car going the wrong way down a one way street or a pedestrian on a freeway, you still must stop. Some people care more about the legal consequences to them (e.g. loss of licence), rather than helping someone and potentially keeping them alive, instead of leaving them to die. Some people think they can get away with it, so they don't stop. The law should be changed so that leaving the scene assumes the driver is drunk/drugged in the highest category, distracted, using their phone, etc. and penalised accordingly. The law should also be changed so it is viewed as a serious aggravating factor in the collision (as above) and charged/prosecuted at the higher level of crime, e.g. culpable driving rather than dangerous or careless or negligent. To send the message that leaving the scene is never acceptable, penalties need to be increased and enforced.
3. Culturally, and the courts reflect this, road trauma is seen as inevitable, to a large degree acceptable, and an "accident" that could happen to any one of us as a driver. (Not the death/injury, unfortunately the thought there is that it will never happen to us, but that being the cause of the "accident" could unintentionally happen to any one of us). The truth is, most road trauma is due to driver error, so it is not inevitable and it is largely preventable. However, until societal attitudes around that change, it will remain accepted as an "accident" and "unavoidable", and things won't improve.