Why Weapon-class destroyers took so long to complete

Why did Weapon-class destroyers take about 42 months from laying down to commissioning?

They had limited priority, lost their main Pacific-war rationale, and were completed more slowly after wartime yard shifts ended.

The destroyers were experimental enough to lose priority to ships required more urgently during the war. Their strongest operational justification was reinforcement for the campaign against Japan. Once Japan surrendered, there was no reason to accelerate them. Shipyards also cut expensive overnight shifts after the war, so reduced labor intensity lengthened completion while saving money.