I think the biggest barrier in programming is just how abstract and alien it is, cognitive load can be enormous. Try to teach engineer about materials or steel liquation or semiconductors - it might be abstract or complex but at least it is dealing with real life physical processes.

With programming it is whole different galaxy. Like explaining pointer arithmetic to someone who just started learning CS. Or recursion, or asking someone to rotate tree in their head - there is a huge chance it will simply BSOD them. Programming is much more close to theoretical physics or maths than engineering.