Considering how difficult it was for Finn to leave the First Order in the initially, returning to them in order to serve the Resistance is easier said than done, according to actor John Boyega.
When speaking with IGN about Finn's more secretive mission, Boyega joked, "Well, it's like imagine you work at McDonald's. You push your manager into a chute compactor and then a year later you decide to go back dressed as one of the colleagues. It's not the best situation."