Because the level of tragedy in his own world is existential in scale, his karmic resistance is off-the-charts for most other universes, now. Madoka, Shingeki no Kyojin... heck, put him in Evangelion or Gurren Lagann. He'll clean house and nobody important will have to die!
Lol , now they are doing with SnK , i remember the one with Madoka Magika , what next Guts in every anime/manga ,especially and mostly in those ones that are darker and usually have more tragic moments ? To be honest i wouldn't mind .