USFS campgrounds are setup (generally) in places to reduce the damage caused by the public, because given enough people, the ‘public’ becomes abusive and we can’t have nice things. And in many areas, there will always more enough people that it will cross that threshold, regardless of what anyone calls the place.
USFS campgrounds in truly remote areas excepted, but any available camping near a highway is going to be a public safety hazard quickly without someone responsible for keeping it clean and somewhat organized/policed.
USFS ‘managed’ campgrounds generally were setup where there was already a problem area.
So are you proposing Rangers sit there and drive anyone away trying to do what they want to do? Or we turn these spots into National parks? Because just saying ‘dispersed camping’ doesn’t work either without someone sitting there enforcing it.