Why attempt to even show what happens after death?
Closure. The entirety of the flashsideways were about the characters working through their issues- Jack proving to himself he 'had what it takes' to be a better father than his father, Kate finding people who accept her for what she is, Sayid learning that he is a good person and he didn't need to cling on to Nadia to validate himself, etc.
I don't even know why some people were there and some weren't.
Watch "The New Man in Charge", it's an epilogue thing and kind of touches on this. But basically they had to be ready to move on and had to consider each other the most important parts of their lives to end up together like that. Not everyone did.
I don't know why so many people hate it myself, it ties together the character arcs nicely.
But this board mostly hates the finale as a whole.
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