Why Italy abandoned the compliant Trento proposal

Why did Italy not use the treaty-compliant 1923 preliminary Trento design?

Because Italy understood that other powers were not observing treaty limits strictly in practice and chose not to impose a unilateral disadvantage.

Published displacement figures were widely distrusted in this arms-control environment. Italy recognized that other powers were exceeding treaty expectations through weight, armor, or interpretive devices. Britain often stayed within literal wording while shaping that wording to preserve room for preferred designs, and American Lexington-class carriers became notably overweight. Italy therefore had little incentive to handicap Trento by remaining uniquely strict.