What's good for supermodels is great for tipping vehicles over in the wind: the taller and skinnier, the better.
Imagine a low-slung supercar like a Lamborghini and a full-sized van circa 1976. Maybe the van has wolves airbrushed on the side in your imagination, maybe it does not. Set these vehicles on a highway in Iowa with a storm on its way and the wind whipping like Indiana Jones keeping snakes at bay.
The Lamborghini doesn't have any surface for the wind to push against; each panel has been made aerodynamically slippery, so the wind glides past. Also, it's so close to the ground that downforce helps keep it stuck to the road.
The van, on the other hand, has loads of surface for the wind to whip against. Passengers inside can feel the whole thing rock down the highway. They can probably also hear the airbrushed wolves howling (but then again, that may just be inside their heads). There's plenty of clearance under that van, so downforce isn't going to help at all.
The lesson? Buy a Lamborghini immediately. It's a safety issue.