The science is vestibular mismatch and your personal sensitivity to it. There are plenty of options for VR activities with no mis-matched movement. And there are plenty of people that can handle a mismatch without any problems.
Basically your inner ear and your eyes are disagreeing about what is happening, and historically when that happened to humans, it was because they ate the poisonous berries. So eventually the people who randomly had the gene where that mismatch leads to throwing up were more likely to live to procreate.
But the brain can be trained, if you are susceptible to VR sickness, play until you start to feel the first minimal symptoms (varies per person, but commonly; warm face, inexplicably sweaty face, or mild dizziness) then immediately take a break. As you continue to do so successfully you’ll notice the response takes longer to come into play and is milder when it does. And if “the berries” keep not killing you, your brain will assume you know what you are doing and don’t need to be protected. But every time it does get too bad, or worse does lead to throwing up, it will reinforce that your brain saved you and it will start coming on more quickly and strongly. Still totally reversible, but best to avoid it if possible.
There are some people who don’t have the response to start with, in my experience it has a surprisingly strong corellation to people with autism, which was nice for us autistics in early VR. We had the whole place to ourselves, hehe. But hopefully we never have to actually worry about poison berries.