I mean, sure, if you have a sufficiently bonkers view on performance metrics, then, say, index finger diameter could be a performance metric, but in terms of things which could actually be seen by any reasonable person as a KPI, lines of code ain’t one.
Have you MET middle managers in the wild? As I said, most of these metrics are measured because they are easy, not because they are useful. The incentives at that level are to come up with some sort of metric and browbeat people into making it; the incentives for the browbeaten are then to make the number. Doesn't matter what the number means.