I see the reason for a memorial but why use the government to steal it. The victims families have been well compensated as humanly possible. The greed is to no end.
The land became, through the Fortunes of War, a battlefield where American heroes died defending America: Preventing the destruction of the U.S. Capitol Building, to be exact.
Once the Fortunes of War choose your Cornfield or your Dunker Church on American soil to be such a historically significant battlefield, the U.S. Government will likely end up owning it as Hallowed Ground.
That is the way it has been since long before we were born and it was not wise to try to get top dollar for the land.