Wonder if it was for ease of manufacturing (less need to form the metal sheets) or for styllistic reasons.
The Citicar / Comuta is similar: https://en.wikipedia.org/wiki/Citicar
The Citicar / Comuta is similar: https://en.wikipedia.org/wiki/Citicar
On the other hand, they were made from fiberglass or "plasteel" (a composite of fiberglass and steel), and I'm not sure how mouldable that material is.