I assume motorhomes and caravans are stuck in the same sort of design rut that computers were in the days before Jony Ive came along.
European caravans seem to have made at least some concession to ærodynamics and are a bit more wedgey than of old. Their USAnian equivalents, Airstreams and teardrop campers
1 apart, are still very much utilitarian wheeled cuboids set high above their wheels and matched only in mass and drag coefficient by the monstrous fifth-wheel campers that tower as high again above the six-foot tall full-sized V8 pickup dragging it along.
1: My grate frend Mr Mueller tows one behind his Mk 1 Mazda MX-5, which must drive the rednecks apoplectic