So someone please explain why aircraft engines have higher failure rates than car engines.
Bluntly, because aviation safety management has shot itself in the foot.
It's very expensive to change anything in aviation, particularly when it comes to the critical bits of an aircraft. And anything that
might perform worse than the status quo is rejected. As a result, aviation is stuck with the status quo -- and for engines that means the ones that were designed in the 1950s -- which are probably considerably less safe than a modern alternative. But no one can afford to prove it.