The maintenance is minimal but repair is much more expensive. Not even talking about the gearbox itself. Consider a damaged rear rim - you'd need to re-lace a n

The maintenance is minimal but repair is much more expensive. Not even talking about the gearbox itself. Consider a damaged rear rim - you'd need to re-lace a new wheel on your expensive hub, which is a lot of labor even for a bike mechanic at $25/h. And repairing the gearbox itself is not something the aforementioned bike mechanic can do at all. Even diagnosing issues with it is an endeavor. On a derailleur system everything is in the open, problems are obvious and parts are cheap and easily replaceable. Also, for the low end the price is prohibitive: there is a firm (Priority) selling relatively cheap, casual belt driven bikes in NYC, which, I figure is quite flat, but the gear ratios on the cheap ones are not good enough for someplace hilly. And for the high end the weight is insane. One does not need to be a "weight weenie" to feel a ~2Kg hub spinning with the wheel.