One Big Problem is Kamen and others thought can/should run on Sidewalks etc except that most places already ban every "motor vehicle" and more. You can't run a bicycle, scooter, and many other unpowered things on sidewalks in many places either.
Many places changes/updates to rules/laws to specifically ban Segway to make no doubt was illegal on public walkways and roads.
So for that and other reasons most of the Public didn't want them, mainly only niche markets and many of them only need a few units.
Kamen left/remove from company over 10 years ago.
Since 2015, Is owned by Chinese Ninebot Inc
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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)
The Ogre's Fiero Cave