Maybe they are trying to keep someone from skidding on the oil. I saw a horrible accident a few years ago when after a light rain a car with a pregnant woman skidded on the mixture of oil droplets on the road and rain, killing her and her unborn child.
Any oil that the Christians applied to the road would be miniscule compared to the oil that drips from cars and trucks that travel that road every day.
Blessings come from God, not oil. Blessings are rescinded by God, not foolish self-righteous academics with their "unholy water".