I looked a little bit further in to it:
I made this route with a reversable road. https://www.openstreetmap.org/directions?engine=graphhopper_foot&route=52.34188%2C5.17382%3B52.31779%2C5.09539#map=14/52.3287/5.1354

if u look OSRM doesn't take the reversible road but grasshopper does unless grasshopper has live data of the current direction of that road it doesn't make sense to send it over a road that might be closed. If u don't know what direction a reversible road is then u can better not send the user there. For that reason is makes more sense to make the ferry alternating since u can wait for it to change direction. and the route example above u can't wait for it to change its direction.