I think maybe it might have been because people trusted the reliability of the Japanese bikes over the Italian machines of the day, plus they were more costly and dealerships were few and far between.
Probably today, a similar machine would sell in higher numbers proportionally.... if the price was competitive enough.
Actually, looking at the CBX and the SEi today, i'd go for the SEi. I think it's aged better aesthetically......but the bike in the video is on another level of tastiness....