Something like a jet plane has a million things that can go wrong, so it is very difficult to counter everything that can happen, and some threats we just scratch our heads and have no concrete solution at all..... bird strike for example.
Elevators mostly never fail because the risk factor is clear and simple - falling, that's pretty much it.
So you know what can go wrong, then its very obvious what fail safes are required, so simple, only laziness or cheepskatedness is powerful enough to overcome it, and even then its very rare.