Cars rolling running through stop signs at like 15 mph is the most common near-miss I have. It happens weekly actually.

I find it extremely common to be heading, say Northbound on a thoroughfare/through street (i.e. no stop signs, bike designated street) at 17-20 mph and with the right-of-way, only to have a Westbound car come flying up on the right (from the East), quickly (if at all) glancing to their left (South, the direction I am coming from), and then immediately turning their head to the right (North) as they try to blow through the intersection all in one motion. By the time the turn their head back to their left to check if there's actually anybody there, they've already committed and it's too late.

They intuitively respond with the typical "it's your fault I'm not obeying the rules solipsism" after they are shocked into slamming on their brakes 3/4 of the way into my lane after I literally scream "STOPPPPPPPPPP!!" to prevent them from hitting me.

As to why it happens? My personal observation is that people in cars are not only distracted but in a hurry. In an unnecessary hurry actually and very presumptuous (presumptuous that it's the responsibility of everyone else to obey the rules/law but not them), because the same thing that motivates them drive their eyes into their crouch as they incessantly check their pointless twitter while drifting into the shoulder at fifty is the same thing that makes them horrible drivers before they ever get behind the wheel: egocentrism; zero attention span; inability to understand, respect, and follow rules (we call it being an adult where I'm from and unfortunately most people never grow up to become one); and of course the bizarre and uniquely de-individuating process that comes from sitting in a hermetically sealed box that can go 100 mph in 10 seconds by moving your foot 3 three inches.