I think they fulfil a need, but we haven't figured out how to integrate them properly. There is something to the idea of essentially using an electric drill motor and battery for transporting someone a few miles - especially when the vast majority of car journeys are under 6 miles, and most people don't want to walk or cycle that distance.
Probably bringing them into line with ebike regulations would help ie road/cycle paths only, 15.5 mph, bigger wheels etc.
I think there are also handling difficulties which are more difficult to resolve. There's a reason why most adults don't ride traditional scooters, and why bike geometry is different to a scooters. Maybe lower speed limits - say 10mph might help here (still quicker than walking, but fewer consequences in the event of losing control).