Actually the did destroy most of the convoy - you just were not shown images of it or missed them them they were.
There is no point in wasting resources taking cut off Russian troops - this is not your Insurgency ... this is a different sort of war.
They will surrender when their stomachs start to growl or when they start to freeze in the winter.
They didn't in Stalingrad.
Not pretending to be some great military tactician. But the Dnieper is not the English Channel or the Formosa Straits. IMHO The Russians could use small craft at night to evacuate the bulk of their troops. It just appears that this unique tactical opportunity does not occur often in war. If the Ukrainians won a great victory at the Kherson Beachhead by capturing or eliminating that force, it very well might mean the end of the war. The land itself is not the prize, its the Russian troops. Try to imagine the political consequences of photos of thousands of disarmed Russian POWs.