The issue with SLOC is that it's an easy metric to game. Being productive does not equate to producing more code. So the way I've explained it to people baring what Skilldrick said is this:
- The more lines of code there are the more complicated something gets.
- The more complicated something gets, the harder it is to understand it.
- Before I add a new feature or fix a bug I need to understand it.
- Understanding takes time.
- Time costs money.
Smaller code -> easier to understand -> cheaper to add new features
Bean counters can understand that.