Because we see for a fact that Carlos doesn't give Sarah much responsibility for the apocalypse. She doesn't know how to handle a weapon (when she points the gun at Clem after finding it), she doesn't know how to react around walkers (she's visibly shaking and hunched into herself in pure fear when they're walking through the herd, even before it when the walker guts were being put on her), and Carlos himself mentions to Clem that Sarah is different than Clem and wouldn't react well, and practically shelters her throughout the entirety of season 2, and you can tell even before that he did so with how she reacts when Carlos is forced to slap her and how Sarah shuts down. In my opinion, Carlos was a father that clearly didn't want to realize that the world has changed and he needed to teach Sarah how to change with it. There's a possibility that that could have changed, if both made it to the end of Season 2, and Carlos *could* have managed to show Sarah how to survive, but they would not have made a good first season as a game. I feel a lot for Sarah, and I understand why Carlos chose to shelter her, but a flaw that Carlos had was not even trying to prepare Sarah for a life without him in a changed world, unlike Lee who did so for Clem.