Can you cite this? Because it's certainly legal for pedestrians to use the roads in my state, sidewalk or no.
There's no massive inefficiency, the cars pass the pedestrians, the cyclists, the skateboarders and all the other road users, when safe to do so, just like the law says they should.
I think most non-freeway roads technically allow pedestrians (with local exceptions), but under strict rules that place them well outside the flow of traffic. I'm not aware of any areas where pedestrians can walk with the direction of traffic while occupying a lane.
There's no massive inefficiency, the cars pass the pedestrians, the cyclists, the skateboarders and all the other road users, when safe to do so, just like the law says they should.