There’s a reason passenger planes’ safety engineering is so much better than passenger cars’: if your car just goes completely dead, you can probably still steer it somewhere safe and get out. If something goes wrong with a plane and there’s no backup system, it’s just become a glider with one chance at landing wherever happens to be available. If your flying car is in the city (and most cars are in urban areas, because most people are) there won’t be anywhere available to land, and it’s going to hit a building. If the pilot fucks up then it might be worse than a glider and just drop out of the air like a stone.