Jensen Ackles, star of Supernatural and executive producer of The Winchesters, has explained the multiverse twist in the spinoff's season 1 finale. Ackles said that it would have been a mistake to try and box The Winchesters into the established timeline of Supernatural, and the only way to make the story work within that timeframe was to create a completely separate, alternate universe. This approach allows The Winchesters to explore new directions for John, Mary, Dean, and Sam while maintaining the character development and personalities that made them fan favorites in the original show.
