Why a purpose-built naval fighter was not produced

Why was a purpose-built prewar Royal Navy fighter not produced instead of converting the Spitfire into the Seafire?

Time, money, development effort, and Air Ministry priorities kept the purpose-built project from production.

The aircraft existed as a prewar concept, but turning it into a service fighter required time, development effort, and money. Air Ministry priorities made those resources difficult to secure. Institutional and budgetary barriers, rather than a flaw in the airframe concept, explain why the Royal Navy entered the war without the purpose-built fighter envisaged in the question.