I think it gets traction with self-driving cars because people, stupidly, expect computers to make perfect decisions 100% of the time. This idea runs into a logical inconsistency when presented with a scenario in which there is no perfect decision. Rather than confront the fact that it's unreasonable to expect perfect decisions 100% of the time, people try to come up with a way to declare a perfect decision in a no-win scenario.
I don't think it's that people expect perfect decisions.
You are right that it essentially never happens with humans. But why doesn't it happen with humans? I think it is because if we are driving down a highway at high enough speed for this issue to arise, we probably aren't going to be aware of what is in our swerve path, and even if we are we probably don't have the time to recognize that we have to make a choice, nor the processing power to make such a choice.
Hence, there isn't really any need to consider this issue with human drivers because humans cannot make a decision in such a situation.
Self-driving cars, on the other, should have the sensors and the attention and the processing power to take into account everything to the side of the road in addition to what is on the road. With them, unlike with human drivers, it is actually possible for them to make a decision in these situations.
I think it is getting traction simply because with self-driving cars, unlike with human driven cars, it is actually a meaningful question. It's meaningful even if you assume that computers don't make perfect decisions--they at least have the time and data to make a decision, unlike humans.