The way it works behind the scenes, is that when you insert a line between line 10000 and 20000, the new line becomes 15000, insert a new line again, it becomes 12500 … and so on and so on. You can actually run out of line really quick.
So just dividing with 10000 won’t work. It might work, but you’ll get line numbers 1.5 and 1.25 and 1.12 and 1.06 …. And that doesn’t really work.