Why the US Navy's 5.4-inch gun went nowhere

Why did the US Navy's 137 mm or 5.4-inch gun project fail?

It was not pursued because established 5-inch systems offered a better overall balance, and later needs led to the 5-inch/54 instead.

The project was never developed far enough to fail in service. Its heavier anti-surface shell had to be weighed against fitting more 5-inch/38 guns, whose rate of fire and dual-purpose performance were already useful. The calibre sits in a persistent Goldilocks problem between destroyer and cruiser weapons: shell weight, mounting size, anti-aircraft handling, and numbers aboard all pull in different directions. A French comparison suggests that the 138.6 mm gun became workable because the Marine Nationale persisted through a long development programme rather than abandoning the calibre after early difficulties.