I don't know, maybe? All those sound plausible but then you have to try and justify each of them with some kind of evidence of some sort, otherwise you're just playing the guessing game.

Now, I don't like guessing. When Russia entered negotiations the war was clearly not going its way, so the obvious explanation is that Putin wanted to disentangle from it with the least damage to his image as possible.

The question is why the negotiations failed, if they were really as advanced as suggested in the articles I linked above. Since the name of Boris Johnson has been brought up (in the context of being one of the Western representatives that told Zelenskiy to drop the deal) I tend to believe that a peace deal failed because at least one side in the negotiations was incompetent fools who should have never made it in power. That the other side is probably the same makes no difference.