Why didn’t the Germans just encircle Stalingrad and starve out the Russians?
I’m guessing that the Volga was a bit of a problem. That and establishing a line of supply and communications as the rest of the German forces head for the ultimate objective – Baku and the oil fields.
They didn’t need to do any of it except mask the Russian formations with a ‘flank guard’ whilst driving into the Caucasus. There was absolutely no reason to go anywhere near Stalingrad, except for Hitler’s obsession with the name’s symbolism.