Humans are not computers. And the fact that computers won some of those games is further evidence that, while Carlsen had winning chances, the position was complicated enough that one or two suboptimal moves might be enough for Fabi to capitalize and win.

A slight advantage in a complicated position with lots of tension and many ways for the game to continue is wildly different from a slight advantage in a quieter position with many of the pieces traded down. In the latter, a mistake might cause you to draw rather than win. In the former, a mistake might cause you to lose outright.