IIRC, the first military burials were near the mansion and included the son of a Union major who had vowed that his son’s grave would prevent the Lee family from ever getting their property back. The price of treason he called it.
Vindictive. Lee wasn’t even CO until more than a year after. It was simply nice and close to the gov and they wanted to stick it to him. Losing DC territory to VA didn’t help, either.