I don’t know the exact contract between these two companies, but often times a publisher like Sony will own the title/world/story and the developer will own the code. Sony is within their legal rights to make a remake of Demon’s Souls (also a Sony exclusive from back in the day), but it seems to have upset FromSoft, and when FromSoft is putting out bangers like Elden Ring, you don’t want them to find a reason to not put their games on your console. Other than Demon’s Souls and Bloodborne, every other modern FromSoft game has a different publisher, whether it’s Bandai-Namco or Activision.