Who is the only president to be buried in Washington, DC?

It is part of the tradition of the Washington National Cathedral that burials of prominent people happen there. Woodrow Wilson is not the only prominent person buried in the Cathedral, but he is the most prominent. The designers and architects of the National Cathedral always intended for the bays on the side to be, in part, memorial bays - places for tombs. (There are only two ways to be interred at the cathedral. One is to be in a tomb - a big marble box. The other is to have your ashes interred in the Columbarium after cremation).

Originally Wilson was interred in the bottom level, in the bethlehem chapel. But he was moved in 1956 to the Wilson Memorial Bay, in the main cathedral.

At the time he died, this kind of burial was the most appropriate and represented Wilson's long public service. No doubt the family and those government folks making the decision decided that the Cathedral, at that time still under construction, was the most appropriate place. Since then the fashion in presidential burial changed - most current presidents are buried in the location of their presidential library. No doubt fashions in presidential burial will change again.