Why Britain developed the Nelsons' 24.5-inch torpedoes

Why spend money developing 24.5-inch torpedoes when they were used only on the two Nelson-class battleships?

They came from G3-era work and were considered for other capital ships, cruisers, and even a proposed HMS Eagle torpedo-carrier conversion.

The heavy torpedo was developed for a wider purpose than arming two battleships. Work had already begun for the G3 program, and 1920s assumptions made a top-tier torpedo seem appropriate for top-tier capital ships. Treaty-era modernization plans could also have spread the weapon to other hulls if governments had funded them. Proposals included fitting heavy torpedoes to cruisers and even converting HMS Eagle into a torpedo carrier, showing that the program belonged to a broader, if unrealized, weapons concept.