I think That art has two main part: Intertainment and Education
for example there are many paintings that you enjoy them from their beauties like an painting of a beautiful waterfall!
and we there are also many paintings and drawings that give u some psychological message!
It's the same in every art like Music and Filmmaking and also in making a game!
It's normal that a game has a realistic story and do every thing that give u those informative psychological messages even to kill your lovely characters in the game!
!!!!Spoiler Alert!!!!
I said that somone say somethings like "What happened to the Abby" or like "Why ellie kill all of those people to avenge from abby and let her go at last!" so for the first QU I should tell you that this is a realistic story and There is no need to tell the destiny of characters because the only thing that is important is the sociological and psychological issues and results
and for the second QU I should tell that this story is a metaphor of our real life!
In real life many of us try to punish the people who hurt us... and ellie and abby have war in their minds and souls! They regret from somthings they do and again do the same thing again and again
Anyway I think the story of this game is too higher and more complicated than these people's platform