Computers are hard, but do precisely what they are instructed to do even (unless actually defective). Correctly translating what you want to instructions the computer understands is hard and complex.
Humans are hard, and cannot be forced to do anything no matter the instructions. Individuals may be coerced or motivated or bargained with in specific ways. Correctly translating what you want to instructions the human understands is also hard and complex.
... until that person can't do it all and you have to replace them or can't grow more.