Twilight stepped up for Cozy Glow after her attempted coup, volunteering to take the filly in and help her see the light, sparing her from Tartarus, and she does so purely out of the goodness of her own heart... Yep, no other reason what so ever.
Well, I'm not much of a brony as I don't like the show, but I greatly respect the fans and their work. I often wish the fanbase of some other franchises were as talented and ambitious as the bronies.