Back when companies started tracking LoC output as a measure of engineer quality, it wasn't long before engineers started making their code extremely verbose and needlessly long.
If you make someone's paycheck depend on something game-able, they're going to game it.
And all the goodwill around "collective ownership" is going to disappear in favor of "job security" real soon.
Teach this junior engineer how the code works? Pfft, why? So you can lay me off?