Why are the cpu heroes such jerks?

I enjoy playing random battle for practice and forming a deck and trying things to see how it goes but there's plenty of times when I really have to wonder why they play as they do.

Example of this from earlier, the cpu was boogaloo and I was night shade. For the final round, I had been wheedling him down and had a shroom for two unblocked on heights and both were 5/5 because molekale changed a couple puffs into lillies!
Anyways I'm waiting and waiting....so I know that somethings going on and finally a chickening which wiped all but the two shrooms and then he uses the supertrick to destroy a damaged plant draw a card, then uses his signature super on the other shroom....and then after everything, he dropped a bungee plumber on my head to kill me since I was at one life.
So why not just use the bungee plumber and end me without all the rest?
Am I to assume that since someone programs these cpu on gameplay, that most players would kill all the stuff first before putting the hero out of their misery?
For what reason? To feel like you got the best of the other players to show that to everyone else