Rocky not appearing in Creed III was big new on its own, but Sylvester Stallone's absence also had the effect of breaking a major Rocky franchise trend. While the franchise's main focus has shifted over to Adonis Creed since the start of the Creed movies, Creed III was the first time that Rocky wasn't in the movie at all, with him having appeared in every Rocky movie up until then. Sylvester Stallone's Creed III absence was sad, and it is made even more so by the fact that it broke one of the series' biggest records.

https://screenrant.com/creed-3-sylvester-stallone-missing-ruins-rocky-movie-record/