For a show that was always about being more than a TV show, the Lost series finale was, in the end, just a TV show. Rather than treating the last six years like a logic problem or jigsaw puzzle that had to be solved and proved, the producers focused on giving the characters the resolution they had been denied for so long, and closing the book on them as firmly as possible.
There was a time when we all thought that Lost might the show to do the impossible: spin out a big science-fictiony epic tale and resolve it in a way that makes real sense, all while juggling its unwieldy cast of characters and giving them all the backstory (and forestory? and sidestory?) they deserve. In retrospect, that might be too much to ask of a show that introduced a smoke monster and a walking paraplegic in its pilot, and just got crazier from there.
In the end, they chose to jettison sense-making for character, which for my money is always the right choice.