I've never ridden a segway before, but I can honestly say i've always secretly wanted to. Damn people look silly riding them, but they way they just effortlessly glide along looks fun to try at least once.
I think the marketing approach they took was part of the problem. I remember early segway ads and stuff, they always took this elitist 'we're going to change the world' sort of spin with their ads that was trying to appeal to a higher end market more interested in fads than anything else. They hooked the 'stubborn early adoptors' while alienating the larger market. At least in my opinion.
This is how their marketing always came across to me and probably helped form my opinions on segways and similar vehicles in general and I doubt I'm alone in my views.
The funny thing is, I bet if they'd found a way to appeal to the extreme sports market they may have found a small niche for themselves. Strange vehicles like this seem to keep a strange second life in that market.
I still see people occasionally riding those razor scooters that were popular for a while in the early 2000's, but, it's always people that are really good at them have spent lots of money customizing them and use them for trick riding. And of course, the skateboard, which has gone through a ton of designs and incarnations, but has been kept alive for half a century or more by people pushing it do the limits. Despite being fairly impractical for primary transportation and I tried for a while as a teenager.
I'm not sure if segways are the best for this, but I bet with some effort, they could have created a small market there that would probably still be popular.
On that note though, I do still see a fair amount of people riding devices clearly inspired by the segway, those handle-less varieties and other gyroscope balanced things and such. So, I think they're not dead so much as they've evolved and the concept of 'personal electric vehicle' has grown beyond what the segway originally was.
I do feel like the electric vehicle future they marketed is coming, they're just not the leaders they told us they'd be and instead of one strange new thing, we've got a variety of things now and on the horizon.