Human nature. Just like how when you're driving in heavy traffic, if someone sees a gap in traffic start to close, they feel obligated to try to squeeze in at the last second. Even if they have absolutely no need to be there. They don't want to get "left out".
And how when you're on your bike, people actually speed up in order to position themselves so they can squeeze you off the road, such as when another vehicle is approaching from the opposite direction on a narrow road.
Self driving cars? How could they possibly be any worse than moody selfish humans, whose driving decisions are mainly made by emotion vs. logic?