Why G3 and N3 were not the Royal Navy's whole building plan

Why assume Britain would build more than seven battlecruisers and a few N3/G3 ships without the Washington treaty?

British orders were incremental, its yards already existed, and fast battleships would not necessarily remove the need for still faster battlecruisers.

American programs were announced years ahead because congressional authorization made a large batch public, while Japan's limited infrastructure encouraged similarly long planning. Britain instead ordered one class and developed the next without publishing a single sixteen-ship ceiling. Existing competing shipyards allowed that incremental approach, so the announced G3 and N3 groups cannot be treated as the whole future fleet. A 28-knot fast battleship could perform some battlecruiser tasks without eliminating demand for a 35- or 36-knot ship in a global navy. Lexington's economic-warfare and reconnaissance design would remain useful, but it was poorly suited to a peer fight against G3. Figures such as Frederic Madden were considering much larger carrier and battle-fleet structures than the orders visible at the Washington conference.