I don't think I really agree with that characterization. To take PCB design as an example, you could just as easily say that once you have your blueprints (i.e.

I don't think I really agree with that characterization. To take PCB design as an example, you could just as easily say that once you have your blueprints (i.e. manufacturing files) then you're done. I see two big differences between SW/HW. The first is that software has a free and fast iteration loop whereas that same feedback loop would cost 2+ weeks and $10k on a PCB design. This makes it so that upfront design and analysis is more reasonable than try it and see. The second is that SW team structures appear to be much more coupled and interdependent. Multiple hardware designers can work for months on the same project without having to communicate much with anyone whereas this seems rare for SW teams. This causes the interdependencies between personnel to be highly predictable even if the work itself is not predictable.