The left lane can be filled with water coming in from the shoulder. Those in that lane can find their car hydroplaning over the water. I would see it a safety issue moving out of that lane while trying to navigate pools of water. Slowing down that lane prevents others from flying through and going out of control in a sudden hydroplane. Having to slow down and waiting for the lane to the right to open up is hard to do safely. So, as a safety measure, slow down, stay in the right lane while you safely navigate the pools of water, slow other down behind you, keep an eye open for an opportunity to get into the right lane safely.
Got it?
Water pools on the right side from my experience, there are a lot more water inlets in the middle of the road, at least where I drive.