Doesn't explain why it's also on in N.
After driving electric cars with noisemakers for over 9 years I can tell you that nobody listens to the noisemakers anyway (they don't listen to regular gas cars either). They continue walking down the center of the parking lane while I'm right behind them for a good amount of time before noticing. I'm no better. I've been caught by total surprise walking alongside the railroad tracks by a 10,000-ton freight train that I didn't hear until it was next to me.
I didn't much care for the driving sound of the Leaf and thought it seemed a bit loud, but didn't think too much of it until the other day when I pulled up to a friend's house and he came outside before I could even let him know I was there because he could hear the noisemaker inside the house. That's too loud. I do not want to be driving around the neighborhood making everyone listen to my "spaceship" soundtrack inside their houses. It was also kind of dangerous because I found myself wanting to drive faster to get it to shut up. In my car it doesn't go away until about 30 mph, so I was driving faster than I'd like to on small residential streets just to avoid the noise.
It's one of those things that seems like common sense, but it actually turns out not to be the case. Human nature is such that people lose situational awareness and there's no possible way to mandate they stop doing that.