Kiev knows that they are lost. Might as well go out with a BANG that shows everybody how much of the aggressors they really are.
Kiev might have conquered Russia at some time in the past, but you see that the Russians have straightened things out.
it is not easy to understand what will happen in future times, things could change and they could happen quickly, the fact is that Putin seems to be focused and going straight in his decision, so the war will happen and it also seems that he is intent on winning it