The problem is in a car, your body is actually moving and your sense of movement aligns with what your eyes are seeing. I’m not an expert but there’s something about fluid in your ears moving?
When it comes to gaming on a flat screen, your eyes are interpreting movement but you are not moving. This, from my understanding is what causes the motion sickness.
I can’t use these VR headsets because they make me sick and give me migraines. I’m just fine playing on a TV or monitor though.