Praise be to Allaah.
These ropes do not usually absorb the najaasah (impurity), and clothes are not usually put on them except after they have been washed, in which case they are pure (taahir), and they are usually wrung out after being washed, so their wetness is removed or reduced. Even if there is some najaasah present, it dries quickly, and with the sun and the wind the traces of najaasah will be removed and will no longer be noticeable. So there is no need to go to extremes in avoiding it. And Allaah is the source of strength.