Why was Hood expected to serve longer than Repulse?

Why did Royal Navy planning allow Hood to serve until 1952 when Repulse was considered useful only to about 1943 or 1944?

Hood had not served in the First World War, and the 1952 date was a contingency if new construction or fleet numbers required keeping her.

Hood had not accumulated First World War service in the way Repulse had. Her projected survival to 1952 was conditional rather than a firm design-life judgment. If replacement construction lagged or required fleet strength remained high, planners might have kept her in service longer than preferred.