0. The obvious answer first off: cell phone usage while driving.
1. We treat driving as a right rather than a privilege, partially because our car-centric infrastructure makes driving essentially a necessity. And so people legit argue in favor of being soft on DUI's because being hard on DUI's can ruin someone's life because they might be unable to get to work, meanwhile they say nothing of the lives ruined when they hit someone.
2. America's culture of rugged individualism leads to selfish attitudes, which on the road means acting like you own the road and everyone else is just in your way.
3. Overall leniency on crashes. If someone crashes into someone because they ran a red light, they usually only get a ticket for running a red light unless they killed someone, in which case they'll get charged with vehicular manslaughter. But no, that crash needs to come with charges for property damage. If there are any injuries require medical attention, they should come with charges of vehicular assault. In short, being at fault for a crash needs to be PUNISHED.
4. Lack of driver's ed. PARENTS SHOULD NOT BE THE ONES TO TEACH HOW TO DRIVE. By not having a standard curriculum, there are often gaps in driving knowledge, or even worse, myths passed down. For example, a buddy of mine was told specifically by his mom to just stay in the left lane if his exit isn't coming up, when the reality is that you should be keeping right except when passing. Also, driver's ed needs to include practicing emergency maneuvers, especially on wet pavement. (EDIT: One thing that would be nice to have is make students complete an obstacle avoidance course in both a large SUV and a small sedan. I imagine we might change minds on what type of vehicle is safest if more people were able to get an appreciation for the agility of a smaller car and learn how to avoid a crash entirely rather than thinking they need to get a 2025 Chevy Movie Theater to be safe, but alas, this would likely make driver's ed way too expensive)
It seems like people just accept crashes as part of life and act careless on the road, rather than treating driving for what it is: Operating a 3000+ piece of metal, frequently at high speeds.
I watch a LOT of dash cam videos on YouTube, and I'm rather passionate about this topic. It's utterly ridiculous how completely careless some drivers are. Changing lanes without looking, making right turns from the left lane, making sudden U-turns from the right lane, following too close, blowing through stop signs and red lights, entering roundabouts when there's oncoming traffic, turning left on an unprotected green when there's oncoming traffic, parking your car in the middle lane of the interstate to change a tire, I could go on and on and on...
And I know someone is going to read some of the things above and say that suspending/revoking licenses won't stop people from driving...and my opinion is that driving on a suspended/revoked license needs a jail sentence. If the state has deemed that you are too poor of a driver to be allowed to drive, but you choose to drive anyways, then you're a menace to society and need to be kept out of society for a bit.