That, Anniesantiago IS often the problem
Although there were indoor facilities (sitting area with running water to evacuate waste) as far back as 3000 B.C.E. (the Far East/Middle East), in the main, proper indoor facilities didn't flow into Medieval Europe until the Crusades, when returning knights brought the the idea home. The knights were often among the upper classes, while the commoner was using a pit out back. Even among royalty the chamber pot/cabinet/garderobe was the norm up through the 16th century. At the Palace of Versailles, only the courtiers and royalty had access to these "private" facilities and the commoners relieved themselves behind curtains and in stairwells. When traveling between towns, inns were often spaced at a distance where travelers would be expected to end the day when in a carriage, or on a horse. Travelers on foot would evacuate whenever/wherever the need arose; covering the waste with dirt, stones or branches. Toilet paper was seldom available, or used by the commoner. I can remember that my grandparents used a Sears catalog on the farm
.
This then appears to be the source of the problem. When the Crusaders were exposed (no Joey...) to indoor/public facilities and became accustomed to using them, upon returning home they sought to approximate the same atmosphere (Joey...
) and sanitary utility of indoor plumbing. If one didn't have such a convenience (comfort station), they were made to feel backward, or uncouth. If visiting guests weren't enough, in 16th Century France, the Government of Normandy regulated indoor facilities and their construction in every private residence.
So, with the increase in pilgrims from the big city on Camino, they tend to bring their "civilized" views/prejudices on the environment and their toilet paper.
I agree that there are a whole raft of reasons why evacuation enroute can be disgusting, odorous, unsightly and a biohazard.