I think a good way to explain to non-engineers is look at writing software like writing a novel. How easy is it to measure the amount of good work produced by a writer? How reasonable is it to expect that any two average writers will be able to cooperate and produce a good work?

Then you can ask yourself, how would you help make an organization full of collaborative writers more productive? Would you measure their lines per day? Or would you spend your effort trying to make sure they like and understand each other?