Because I am one of those city bikers. The speedsters, the ones who seem to treat the rules of the road as mere suggestions, zipping past you on the lakefront path with my earbuds in. I apologize perfunctorily now, because I'm not really sorry about that.
I'm sorry that I'm not really sorry.
I overstate my offenses. There are truly bad bikers on the streets and I make a conscious effort to be less arrogant and reckless than they are. I don't obey every traffic law but I do bike by a personal code. I never bike the wrong way down one-ways streets. I always wear my helmet. I signal when turning and I announce that I'm passing on the left (although I only do this if there's no room for me to simply pass with a wide berth, such as if I'm about to be threading a needle between the slow-mover in front of me and oncoming traffic). I slow down at stop signs and only continue through if I'm not trampling on another vehicle's right of priority.
To me, city biking is akin to being a bird flying at altitudes of airplanes. The planes conform to a very rigid and by necessity pre-planned route, designed to get them from one point to another without hitting other planes.
And I am a raptor, who does not get signals from air traffic control. My only directive is to not be in a situation where I am going to be struck by one of these giant metal buzzards. If that means slowing down, if it means swooping in a different direction, I do that. If the sky is open I continue on the path I wish, regardless of signage.
I live, and have thus far survived, by three rules:
1) Avoid being in the path of anything else.
2) Be sure, then be swift.
3) Presume that nobody sees you.
It's a little bit like ninjutsu. Which is part of why I bike. Because ninjas are awesome.