It's no different than when the guy backs onto the boat launch and THEN pulls off the cover, load the cooler and whatever else. All that should be done BEFORE you pull onto the launch.
I just grin and bear it! I guess it happens in all different forms, whether the boat launch or the dump station. I'm ready when I pull up to the dump station as well as the launch. I wonder if those other folks are either newbies (and don't know any better yet) or the ones that do it only once or twice per year and truly have no idea.
A little consideration goes a long way!