I grew up in CA where the left lane is the fast lane. It was jarring to me (and still seems so) to have cars continually jumping between lanes to pass, then return. It also seems like they invariably cut in too close when they go back to the slow lane.
From the California DMV:
Drive in the lane with the smoothest flow of traffic. If you can choose among three lanes, pick the middle lane for the smoothest driving. To drive faster, pass, or turn left, use the left lane. When you choose to drive slowly or enter or turn off the road, use the right lane. If there are only two lanes in your direction, pick the right lane for the smoothest driving. Do not weave in and out of traffic. Stay in one lane as much as possible.