They claim that Justin Lin, who directed Fast and Furious 4-6, might be looking to return to the franchise, and that Fast and Furious 9 is being pushed back to accommodate Lin’s schedule.
The spinoff is being moved onto the calendar in order to keep the franchise going in some form until part nine is ready.
However, The Hollywood Reporter claims that it might actually be the other way around.
The perspective has been that the planned spinoff movie, that has been rumored ever since we saw Dwayne Johnson and Jason Statham on screen together in The Fate of the Furious, was pushing the next sequel down the release calendar in order to make room for itself.