Its all a matter of logistics. The Russian Navy can no longer land troops, supplies and fuel unhindered along the southeastern Ukraine coast. Russian tanks and convoys often simply run out of fuel. However the Ukrainians lack the ordinance to destroy sitting indefensible vehicles.
Try to imagine an American convoy sitting motionless on a Vietnam highway the way that Russian convoy just sat outside Kiev for over two weeks. In Vietnam the VC and NVA would have found all sorts of ways to attack it endlessly. The image that will always remain of this war was that convoy just sitting there unmolested for over two weeks.
I do not think that is an accurate image of what happened on the ground.
“The image that will always remain of this war was that convoy just sitting there unmolested for over two weeks.”
The Ukrainians were hitting them day and night. They withdrew because of the losses, while they still could.