First - the fact that it's played for real money. If I win, I feel like a common swindler stealing money that someone could use to pay their bills or buy something nice for themselves. If I lose, I feel like a swindler's victim. And if the people around the table happen to be my friends - why would I ever wish to victimize them, or ruin their image in my mind by watching them victimize others?
Second - the lack of information. Many interesting games provide incomp9lete information of game state to the players, which one then needs to reconstruct. But with poker, the lack of information is so severe that one has no hope of reconstructing the game state - reasonable possibilities are too many to analyze, one is forced to pretty much guess and make gambles. It's an unpleasant experience.
It seems like a game for people whose brains are wired in a manner incompatible with mine. If I discover that someone likes poker, I find them rather suspicious. And people who teach poker to their own children - like the article'a author - are, to me, utterly incomprehensible.