TL;DR:

The Academy’s rule states: “In cases such as sequels and franchises from any media, the score must not use more than 20% of pre-existing themes and music borrowed from previous scores in the franchise.” Since Zimmer’s composition for “Dune: Part Two” incorporates substantial elements from his work on 2021’s “Dune,” it falls outside of the eligibility criteria.

Hans Zimmer fails to meet the requirements of making a non generic score