Why later US carriers left Lexington's electric drive behind

Why did later US carrier classes switch from Lexington's generator-driven electric propulsion to conventional machinery?

Treaty tonnage made the lighter, denser conventional system more attractive, despite the damage tolerance offered by turbo-electric drive.

Lexington and Saratoga retained machinery designed for the unconstrained battlecruiser hulls from which they were converted. Turbo-electric drive was highly redundant and therefore valuable after battle damage, although it was heavier for a given displacement. Later purpose-built carriers operated under treaty limits, making conventional propulsion attractive even though it surrendered some of that redundancy.