It’s actually a lack of flex in the rim that causes the rubbing. A traditional rim tends to go out of plane (like a taco) when you’re out of the saddle causing a lot of deflection at the road but very little at the caliper. A stiff rim stay in plane with itself so any deflection at the road is mirrored at the caliper, causing the rubbing.
Mavic did a study of this years ago but I can’t seem to find it these days.
Mike