When Gandalf is recounting to Frodo what happened at the Ford of Bruinen, he says that Aragorn and Glorfindel had moved out of the way of the Black Riders to avoid being trampled.
Your friends sprang aside, off the road, or they would have been ridden down. They knew that nothing could save you, if the white horse could not. The Riders were too swift to overtake, and too many to oppose. On foot even Glorfindel and Aragorn together could not withstand all the Nine at once.
Why didn't Aragorn and Glorfindel strike the last two or three Riders as they went by? They could easily have reduced the number of Riders facing Frodo. Even though we see that this wouldn't have been needed, they still should have tried to help in a small way.