Why not simply keep the 12-inch gun?

Why would the Royal Navy fund a 14-inch gun instead of staying with the 12-inch gun already in production?

The point of the investment is a qualitative leap: a 14-inch gun offers a meaningful advantage where the 12-inch gun is already mature and serviceable.

The research fund is intended to seek a qualitative edge. The 12-inch gun is already in dependable production and needs less developmental help. Elswick offers a 14-inch proposal, while other firms also consider 13.5-inch and 14-inch designs. The hoped-for precedent is Warrior and Black Prince's effect on competition with France: a leap large enough to discourage the rival from continuing. In this interpretation, Dreadnought's historical advance had been insufficient to produce that effect on Germany. Funding the larger gun offers another chance at the disruptive advantage the Admiralty wants.