The other members of the O5 finally had enough of Young Jean, booted her to a team that won't stand for her bullsh*t meddling, then brought aboard a clone of the X-Men's greatest foe and a self-hating religious zealot because that's still an improvement.
....
Alternatively, Young Jean realized that she'd done all the damage she could to to her O5 teammates while still alive, and decided to move on to her next target of opportunity like a swarm of locusts looking for other fields to devour.
Lemire called dibs lol.