Yes, but the existence of jerks with offroad vehicles explains some of the fences.
There are plenty of places where just having visitors regularly hike across the ground off-trail does significant damage to the ecosystem, which is why fragile or popular parks restrict public access to marked trails and designated campsites.
There are plenty of places where just having visitors regularly hike across the ground off-trail does significant damage to the ecosystem, which is why fragile or popular parks restrict public access to marked trails and designated campsites.