They are not struggling to understand basic concepts like starting the engine or even what an engine is. Cars have little in their interface that is intuitive. It may be easy to figure out how to activate the turn signals, but it is not entirely clear what turn signals are for unless you have some kind of experience with other drivers in traffic. To the uninitiated, a turn signal is a blinking light that appears to be unrelated in any way to the act of conducting the vehicle through a turn. In fact, given no prior knowledge of motor vehicles, it's difficult to see at first how a car could move you from one place to another at all, unless you actually saw one moving.
Computers are complex devices in a complex environment too.
Computers are far from ubiquitous in real life or in popular culture. Computers in the popular media are often portrayed in a grossly distorted fashion, totally unlike any practical computer in real life. It is difficult to find anyone in real life who truly understands a given computer system, and much harder to get them to explain it in a short period of time. Most of what a computer does is invisible and abstract in the extreme. The only effect that the user has on the machine at all is the tiny part of the system that is exposed by its user interface, and many user interfaces are designed to hide as much information as possible from the user.