I think it's because of the lack of feedback. Humans also can't do much without feedback. E.g. I doubt most people could write 100 lines of code that works first time without even compiling it once.
Indeed. I wonder how much AI will do in industries with longer feedback loops that are much noisier. I think the field of software is a unique field in that sense.
Disagree. When tool limitations meant that this was the way people had to work, many people could do this.
It was much more inefficient, because it's easier to find bugs after compiling or running the code. But it is perfectly possible.