The answer to this is also the answer to where they were created, San Francisco. They’re perfect there because:
Cars are a hassle to deal with for traffic and parking. It’s dense enough and public transit is good enough that you only really need to walk/ride the last half mile.
The hills are no joke, I’m pretty in shape and even I have to walk a bike up most of the hills. This can be helped by an electric bike but that brings us to
Bikes get stolen fairly often. Especially if you have an ebike this will cost a lot in the long run. With a one wheel you can just carry it in the storeand not have to worry.
For most other American cities that are less dense, more flat and have less thefts they start to make less sense.