That is basically because it is near you and far from anything else. So it doesn't have to do anything to not pick up background noise. You can do that with any

That is basically because it is near you and far from anything else. So it doesn't have to do anything to not pick up background noise. You can do that with any mic, headsets just have a bit of an advantage in having a fixed placement right near you however you move. I have a mic on a boom over the monitor so it ends up close to me and I wear headphones so that has much the same effect. But its all about placement.