Some parks, especially CCC built parks in my experience, the length limits are based on the tight roads to get to the side, through the forest.
I've seen several campgrounds with some 50-70 ft long sites/driveways, but without cutting down trees, you are not going to get your trailer into those sites.
I was at one last week. Nice open roads, big sites - and a 7ft 4 inch wide road in one section where the driver had to make a 90 degree turn backing up into the site. With rock, 18 inch deep ditches on both sides of the road. Obviously only small rigs were in this section.