These pictures were taken at the Fukuyama Auto and Clock Museum. ( https://www.facm.net )You have to wonder why the Japanese market was so receptive of three wheeled vehicles. After all it was not just one manufacturer but several that made three wheeled trucks, as they called them. You have to realized that rickshaws were still prevalent and a three wheeled vehicle was basically a motorized rickshaw.Roads in Japan, especially in the areas that were not subject to bombing were narrow. Bombed out areas rebuilt with wider roads. Hiroshima, for example, has very wide roads by Japanese standards. I lived there for a year, so I ought to know. It is a very beautiful city with lots of rivers and parks.
So you can see why a small vehicle like a three wheeled trike would be popular in Japan.
Noted on the History page of the Daihatsu company ( https://www.daihatsu.com/company/history/products_1907.html ):”1971 MAR Begins manufacturing and selling DBC-1 ultra-small three-wheel mini delivery vehicle.”