Look at this [0]
It's an interpolation thing; it's much easier for your brain to do the tracking of an object when it smoothly moves around, instead of it having to do interp / extrapolation, and this should demonstrate why
Can I ask why you think it sounds like a placebo? I don't really see why there's any logic behind 144hz being the ceiling of how well your eyes can see, and 144hz -> 240hz is a big jump