Rey grew up abandoned on a desert planet fighting for survival. She knows what birthdays are, but they're really for other people. She doesn't take part in such frivolous things. (It doesn't have anything to do with the fact that she doesn't remember her birthday, or that it would have just been a reminder that she didn't have anyone to celebrate with.)
Finn has no idea why someone would celebrate such an arbitrary thing as the day you were born. Like, who cares? In the Order they had Ascension days, which were either full of pride and happiness (if you advanced) or shame and fear (get held back one too many times and you would disappear from the program.) Finn was never held back but he still gets a sick feeling when he thinks about the kids who were...
Poe is too old to really put much stake in his own birthday anymore, but when he realizes the other don't even know when theirs are he makes it his life goal (outside of resistance fighting) to make up for lost time.
Rey/Finn/Poe Birthdays
Finn has no idea why someone would celebrate such an arbitrary thing as the day you were born. Like, who cares? In the Order they had Ascension days, which were either full of pride and happiness (if you advanced) or shame and fear (get held back one too many times and you would disappear from the program.) Finn was never held back but he still gets a sick feeling when he thinks about the kids who were...
Poe is too old to really put much stake in his own birthday anymore, but when he realizes the other don't even know when theirs are he makes it his life goal (outside of resistance fighting) to make up for lost time.