Why do some people who drive a car stay in the left lane?

The left lane is supposed to be the fast lane. If you want to drive faster, then use the left lane. Traditionally it is ment to be the passing lane. If you want to pass someone driving slowly in the right lane, then pass them using the left lane, and get back over to the right lane until you need to pass someone else. However, you should not sit in the left lane driving slowly. It is ment to be a passing lane and if you sit out in the left lane, it will make others unhappy! I hope this helped!