We may want to expect the Washington D.C. scenes to follow a new group of characters who start out in the city and then later make the trip to Alexandria or Hilltop.
A big question is why Washington D.C. is being visited in Season 9.
The Walking Dead will presumably need some new characters now that the conflict with the Saviors is over.
There could be zombies everywhere, and everything there is to plunder might have been taken during the original exodus from the city!