More people will visit his grave at his library, most likely. And it brings more attention to his library. He could have chosen Arlington, but he chose the place that emphasizes his fame. What he had was far more impressive than a riderless horse. He had one of the few trains to carry a presidential casket. The organizers of his funeral knew exactly what they were doing, and did the most impressive job of it.
He also wanted to be buried near his wife of so many years. I give him a break on this one.
He could have chosen Arlington, but he chose the place that emphasizes his fame.