Why does the AI current judges are so sweet with the contestants?

In my opinion, Simon Cowell should come back, because he was the only judge who criticized the performance. The current judges just talk about things that it doesn�t really matter. Simon would have said: "Paul McDonald, you NOT sing", "Lauren Alaina, you�re still here because your family pressured the judges for the gold ticket", "James Durbin, we don�t need another Adam Lambert, and you should be original".