One of the main reasons I stuck my geared bike on the trainer and bought a single speed for London commuting - gears are FAFF to maintain. Yes, there's video tutorials, etc., but there's still a non-zero amount of witchcraft going on.
Or automatic shifting for the untapped market of people who wouldn't figure it out but also wouldn't ride a fixie. I can see the concept getting more popular as the price of electric bicycles decreases.