I asked a former truck driver once and his answer was that it's easier to see what's in front of you than behind you. I wondered why people in our neighborhood backed into their driveways at first, then I realized this was indeed true. If I turn into the street and back into my driveway, somebody probably hasn't jumped behind my car. If I get in my car and back out of my driveway, somebody walking/biking along may not notice my car backing out of the driveway, and my old potato backup camera isn't always the best at illuminating people behind my car at night in bad weather.