It's worth separating the momentum M*V you're referring to, from the energy M*V^2 that's dissipated in deformation in the collision.

Hmm I'm not quite satisfied even by my clarification. Car and truck chassis strength needs to scale with something closer to M*V^2, so the truck chassis is multiple times stronger.

Somewhat related fascinating take: A schoolbus driver did a tiktok saying, roughtly: For its size, a schoolbus is a relatively lightweight vehicle. We don't have Mansfield Bars because we don't want to absorb the impact of you running into the back of us and pushing us into children. Instead, you go underneath and the children have a better chance of surviving. Pretty sobering.