Because people honk too much.
There are an amalgam of sounds that come in through my window, drunk people yelling in the PM, leaf blowers and lawn aerators in the AM. But throughout the day and the night, the incessant honking.
Agreed, sometimes you have to honk. I once cleared a traffic jam with a single honk. (Trust me.) But never do you have to honk for ten seconds. Oh, the long honkers. The only thing worse than the long honk is the honk back. YOU DON'T GET TO HONK BACK. I'm honking at you! You're in the wrong or I wouldn't have honked in the first place.
This is why the system of communication from one car to another desperately needs an upgrade. For too long have we been limited to facial expressions, hand gestures, and klaxons. The closest I've come to a feasible solution is a voice-to-text scrolling LCD display mounted on the front and back windshields, so that whatever you have to say can be read (or easily ignored) by offending drivers. I'm sure, however, that the CA DOT would take exception to the idea, and it is rather early 2000's.
Perhaps the simplest solution is a really loud megaphone, or failing that, a variety of coded honks. In example, one honk to say, "Don't change lanes, you'll hit me!" another to express, "I would appreciate it if you would go, instead of texting at this stop sign," which sounds just a little more vindictive than, "You have failed to notice that the light has turned green."
But for the able-bodied woman that starts to walk across the street when there are only two seconds left, then, when she's walking in front of the cars waiting to go, and the light turns green, yet she continues along at her casual pace, you really need a special horn, one that says, "WHAT ARE YOU, SOME KIND OF BITCH?"