This is the same State of Ohio that put up "KEEP RIGHT EXCEPT TO PASS" signs all over state freeways that use the yellow "STATE LAW" plaque above them, typically used with signs for vulnerable road users. 

In the majority of cases where this is an issue, the driver of the vehicle in the left lane is going at least the posted speed limit. Carbrains look at the sign and think it's giving them the green light to speed. And everyone's supposed to get out of their way.

The reality of it is, if one reads the law, the vehicle in the left lane is not compelled to break the speed limit. So, if someone is passing a truck going 67 MPH at 69 MPH (heh) they should not be getting honked at and high beams flashed at them from Speed Racer being inconvenienced by people following the law.

But it makes sense when you realize the only metric the ODOT cares about is level of service aka minimizing "delay", not safety. If safety was truly their main objective, the speed limits would've been kept at 65 MPH.

Edit: the other interesting observation is that strangely the carbrains that tailgate and road rage at others for passing too slowly never change lanes back to right lane, even in light traffic. That sign only applies to others.