Fundamentally, that’s why SLOC can be useful as an estimating metric, but terrible as a control metric. SLOC, FP and so on all have their limitations, but they demonstrate that most of the effort-time in a project doesn’t go into putting hands on keyboard. Conversely, trying to monitor developer productivity with SLOC simply reintroduces the conceptual error that the estimation effort attempts to prevent.
Goodhart's law - "When a measure becomes a target, it ceases to be a good measure."
I used to work for a company that bills their customers for dev hours spent. The software they put together worked fabulously well - in the production of billable dev hours.
