Eh, the slow riders are jerks too :). At a red light, they'll cut the line and blow through the intersection. Then the light turns green and you overtake them until the next red light. Rinse and repeat until you get to work/home.
Not to excuse such behaviour, but it can be explained in part by minimising time sucking emissions which are typically most noxious when a ICE is accelerating. So these jerks wishing to get upwind of accelerating tail-pipes is rational, even if selfish.