Why Britain kept such an awkward Admiralty structure

Why did Britain organize naval administration through this complicated set of boards and offices?

Because historical choices accumulated, especially in the seventeenth century; the system evolved rather than being designed cleanly from scratch.

In this interpretation, Britain's overlapping naval boards grew from a seventeenth-century institutional mistake. Authority accumulated in a commissioned Admiralty Board, a semi-independent Navy Board, and offices with their own royal or political backing. Each part solved a real administrative problem, but their overlap made responsibility contested. Later reform therefore meant fusing inherited structures rather than simply drawing a new organization chart.