He wanted the Army of the Potomac reunited and I think he thought the VI corp was his main strike force. With the VI corp in the trenches at Petersburg the strain on his army was less, and everyone could prepare for the spring final push. The City Point forward depot had become the equivalent of any primary depot, and it was efficient not to run another such depot in the Shenandoah Valley. The US cavalry on the other hand consumed so much forage and fodder, that it was best logisitcally to supply it directly from Washington as long as possible.