Because Messi isn't a person. I don't know how they did it, but he does not have normal emotions. He's like a toddler. He doesn't have the complete spectrum of human emotions, he's not that evolved. It is the very reason one cannot ever support Messi.
You see, emotion is what makes great stories. It is what makes the Iliad complex and wonderful. Pride, honour, but also wrath, pity, rage and anger play a role in the greatest stories of all time. This is why these stories appeal to us. This is what makes us human. Del Piero scoring against Inter a couple of weeks back is just a man scoring just a goal against just a team. But emotions change all that. Del Piero, the ancient warrior defeating his own self doubt and the doubt of others time and time again scoring against our arch enemy in what is probably his last season at the club is a tale filled with emotion, filled with humanity.
Lionel Messi is only biologically human. I do not consider him to be a person.