Likely, because he was thinking of something else. It happens often when playing weaker opponents, you are so concentrated on some genius master plan to defeat an opponent, that when an opponent does something dumb you fail to see it immediately. Of course, my lichess rating is slightly below Carlsen's so I'm probably not the world's best expert on such things.
(I don't quite understand what you mean by 'those conversation would never have happened .. ')
(I don't quite understand what you mean by 'those conversation would never have happened .. ')