The Composer said it's to help the players grow and change. Ah, I say 'said,' but that person was rather insistent that I ask all the question. It was a sort of 'leading someone by the nose' situation.

Moreover, the Composer said that it was because growing and changing, or rather, 'elevating the soul,' elevates the world on the return of those souls to that world.

Yet, this game is unusual. Aside from its length and the presence of Reapers among the Players, as well as Max's role as Host.... So far as I'm aware, there's never been a game that took Players from multiple universes. So its purpose must be larger than that.