Why do people drive like this?

When I was pulling up to an intersection, I noticed that the black Toyota pickup in the lane ahead of me was sitting at the stoplight with his hazard lights on. Thinking I was dealing with a stalled truck, I pulled into the adjacent lane. Surprisingly, when the light turned green, he pulled away like nothing was wrong. Must have gotten it to crank at last, I thought.

But it seems I was wrong again; he kept the hazard flashers on for the next several miles, until he turned off the road I was following. Apparently the driver was simply in the habbit of driving with the hazard flashers on. It's not the first driver I've seen who was doing this, either, driving along at normal speed with no obvious problems but the hazard lights blinking anyway.

Why is it that people drive like this? Are they simply so inattentive that they don't notice the clicking of the relays and the blinking lamps on the dash? Are they trying to warn everyone that they are hazardous drivers?

I just don't get it.