One difference is that there are parts of the system that, most likely, not a single person understands nor, even with weeks of effort, could understand. At least with cars, you can be reasonably sure somebody understands or can reverse engineer any specific component. With certain software that is a lot less possible.

It would be like if our society couldn’t fully function without Roman concrete, but no one knew how to make it anymore. Which is sort of what happened during medieval times: people continued to use Roman roads and Roman bridges. But if anything degraded, there was no hope of repairing it.