I love a challenge so here goes with a few possibles as to why road is not straight. As we look at it this may have never been a Roman road which opens up the argument , 'was this really the route taken by pilgrims?
Now? , lets say the farming even 150 years ago was continuous - there hay have been a haystack , a tree , rocks , anything that would have a horse and mule follow the easiest route? Its a great Question.