For most non-hobby project, the cost of code was in breaking a working system (whether by a bona fide bug, or a change in some unspecified implicit assumption). That made changes to code incredibly expensive - often much more than the original implementation.

It sounds harsh, but over the lifetime of a project, 10-lines/person/day is often a high estimate of the number of lines produced. It’s not because humans type so slow - it is because after a while, it’s all about changing previously written lines in ways that don’t break things.

LLMs are much better at that than humans, if the constraints and tests are reasonably well specified.