Can't defend against Ukraine's advance. Can't locate their HIMARS systems before they skedaddle. Can't deter partisans. Can't perform counter-battery fire. Can't hide from drones. Can't lift sanctions or reduce external aid. Can't train up a functional army and overcome the endemic corruption in their military. Can't replenish the loss of equipment and refit their diminished BTGs.

 

They're doing this because they have exhausted their options, save for provoking a wider war that they haven't a hope of winning. All Russia has left is a particularly nasty flavour of terroristic spite.