I think there are a couple of key differences that you’re underplaying. First, for usage of cars in society, there’s a nice gradual curve where an early slow u

I think there are a couple of key differences that you’re underplaying. First, for usage of cars in society, there’s a nice gradual curve where an early slow unreliable car is still somewhat useful, and a faster car is a bit more useful, etc, and that’s what allowed them to get off the ground (as it were). There’s a vastly higher threshold before jetpacks start being usable and useful. Second, cars are relatively fail-safe in that if you take your foot off the accelerator the car will coast to a halt. Lots of cars can easily come to a safe stop together -- traffic jams are bad but not immediately life-threatening. Jetpacks aren’t nearly as failsafe because if you stop flying you need to land (or more likely, crash-land). Planes have the same two advantages over jetpacks, because even a slow or unreliable plane is useful because it can carry cargo; and most planes can glide a bit which helps reduce the risk of crash landings.