When you say Engineering is not that complex, have you taken into account corrosive sea water, pressure, currents, what it means to make repairs and maintainance down there etc? It is difficult, because it deals with a very complex world full of physics, chemistry and even biology in a way that does not allow errors.
replyEngineering doesn't seem complex because there are centuries of learnings behind it. Those learnings become rules and suddenly it appears "simple" because no one debates whether to use wood or concrete when building an undersea tunnel!
replySoftware isn't inherently complex, it becomes complex. Because it is iterative. Because we keep making demands of it that weren't planned.
replyImagining building a bridge and then in the middle someone comes along and says it should also be a tunnel. I think therein lies a main difference to engineering and software engineering: planning and sticking to a plan.
Another thing are incentives: real engineering has real incentives to do it right, else you will get sued - by the families of those that died. Software engineering does not have this incentive to get it right.