It's notoriously hard/expensive to get a car/standard bike parking space. Even at home, and probably wherever you go if the place has any popularity. Think about parking car in Shibuya.

So a small vehicle has a real intrinsic value, not as simple as a parking a bicycle, but pretty close.

PS: Honda also makes the Monkey, which is ultra cute and pretty popular

https://www.honda.co.jp/Monkey125/