Far too expensive, far too early for the required battery tech, and all the auto-balance stuff ended up being unnecessary added complexity. Per Wired:
Before it launched, the Segway was said to revolutionize the way cities are laid out and how people get around them. Venture capitalist John Doerr predicted it would reach $1 billion in sales faster than any company in history, and that it could be bigger than the Internet. Kamen expected to be selling 10,000 units a week by the end of 2002—that’s half a million a year. In the next six years, Segway sold just 30,000 units, according to Forbes.
Additionally the super-wide format of the Segway is not great at all for cities and sharing space.
The long, narrow “skateboard” or “surfboard” shape of a scooter / bicyle is superior where you need to fit amongst existing pedestrian and vehicle traffic, e.g. in cities.
I think we also see this effect in the brief and now subsided popularity of so-called hoverboards…
.. wide isn’t as compatible with actual transportation needs, and they ended up being harder to use in practice due to the stance, harder to balance on versus narrow scooters and bicycles.
I definitely agree that the electric scooter is realizing the original vision of Segway. But the Segway itself is really a niche design for niche industries:
But it has found a measure of success in industrial and fleet applications where employees are on their feet or moving around a lot, something that makes a lot more sense than personal ownership. Police departments (who have special versions with sirens and strobe lights!), tour groups, warehouse workers, mall security guards, and airport maintenance staff have all adopted the Segway.