The real reason the Segway didn't take off, in my opinion, is that it didn't solve any real problem.
Walking isn't hard for most people; in fact, for most people, walking is among the most pleasant human activities. It's not particularly fast, but when you're walking somewhere, you aren't that concerned about speed. By being slow, it lets you do other things easily -- talk, listen to music, take in the sights and sounds. No one needed "faster automated walking".
What's more, using a Segway to "walk fast" somewhere removes all of the benefits of walking, except the "getting from point A to point B" part. So it's actually worse than the thing it purports to improve. It removes the health benefit; the idle mindlessness of the task (mindless Segway riding is too dangerous); it's more expensive; and, you have to worry about charging, parking, and helmets.
The reason e-bikes are now taking off, by contrast, is that they make perfect sense and solve a real problem. Many people enjoy biking, but some people don't enjoy the strenuous parts of mechanical/manual biking: for example, biking up hills. Further, when you're biking, you usually do care about covering some amount of distance in some amount of time, thus an e-bike helps with that. Many modern e-bike models (like the Bosch, Blix, etc.) combine all the benefits of a normal bike with the additional benefit that a battery provides (making it easier to cover longer distances with limited stamina/endurance/practice). The e-bike is what the Segway should have been -- it solves a real problem.