More a relic of licencing history stemming all the way back to Morgan 3 wheelers and similar from the 20s and 30s[2]. Morgan actually recently re-introduced the classic 3 wheeler. You still find licence, tax, and insurance advantages to 3 wheelers despite them bearing little resemblance to the vehicles that led to the category.
That said, the Smart car was a huge hit in Europe for size, parking and convenience so I don't see why a 3 wheeler couldn't still work.
The difficulty I see is, well the size may be off putting to many but they are likely the same people to be worried about a motorbike. The cost seems a bit high but I haven't looked at the full feature set.
I think it really comes down to a cultural shift, getting people to think of personal transportation being well, more personal in size. For the most part there haven't been alternatives to a full size car and when cost it factored in many two car families cannot afford the third one, the commuter car.
I think their idea of service vehicles is a good idea but that might require areas where there is sufficient charging