Well it's just like life isn't it? You have periods of rest when everything is just so and then you wake up one day and realized everything has changed. Things have to change. You never get anywhere if you keep yourself rooted. In order for the show to stay the same Joan would still have to be naive and she'd seen too many ripples to ignore the fact that God existed. She was changed by everything she'd been a part of and that had to lead her down a different path to new discoveries.