It depends. Hickman writes a lot of Avengers content, so a new writer replacing him may want a big head start.
Sales for non-Hickman Avengers titles haven't been that good, so it could also make sense for Marvel to place the future writer of the post-Hickman Avengers on one of those books, to increase the perceived significance.
It's also possible that the end of Avengers has led to a game of musical chairs among Marvel writers. Maybe Gillen is taking over a book currently written by someone leaving to take over the Avengers.
Or it could be a new title, a spinoff of Original Sin or a tie-in to Axis.