Their guidelines are to preserve the trail surface as it was during the canal operation.
Preserve the trail surface, okay. In many of the images I see from the C&O, clearance between the canal and the trail surface for a tow rope is not maintained. Their definition of "canal operation" seems arbitrary.
That, however, does not explain the NPS’s half ass band aid solutions to the areas that repeatedly wash out...I think the NPS’s problem is more a lack of funding.
Time and again it's been shown that the least impact & lowest maintenance cost is a hard surface with engineered drainage. Otherwise, the mud holes get wider, the ruts get deeper, erosion is continuous and the washouts are eternal.