Motorists: Why Don't You Indicate?

I always use my indicators as a matter of respect and consideration to other road users and pedestrians alike but I'm in the habit of doing it anyway. It's down to ignorance that's all and in their view they think as long as they know where they are going why does anyone else need to know. I agree that it is really frustrating and in my view I think that most road traffic accidents are caused through not indicating thus crossing the path of another vehicle. Many accidents could be avoided if everyone drove as they were expected to on the day of their test.