Jennifer Lawrence could have left the X-Men franchise after X-Men: Apocalypse. Her contract was up, and she wasn't obligated to return. But Lawrence chose to return anyway, for you, the fans, and for Mystique, the character.
In an interview with Digital Spy, J-Law revealed her reasoning for returning for one more X-Flick.
"My contract was up, I didn't have to do another one, but if I didn't do another one, what would her story be? I felt like I owed it to the fans, and I owed it to the character to follow her journey, to be fair to the movies, and not be like, 'I don't want to do another X-Men!' And then I just never show up and everyone's very confused about the Mystique they've been following for the last three films."
If there's one thing that X-Men fans can't deal with, it's confusing storylines!
In all seriousness though, props to J-Law for taking comic book movies seriously. X-Men: Dark Phoenix may end up being as terrible as X-Men: Apocalypse was when it hits theaters in November 2018, but at least we'll know her heart was in the right place.