In the case of Chibnall its quiet obvious why fans are ignoring cannon. He did first. The plot of his run ignored previously established cannon from preceeding

In the case of Chibnall its quiet obvious why fans are ignoring cannon. He did first. The plot of his run ignored previously established cannon from preceeding season and made large changes to the established lore around the doctors origin, and the entirety of Galafray society said and shown on screen. So fans chose to ignore plots from his time as showrunner. Its like when fans of books ignored unfaithful movie adaptations.