Why Implacable stayed close to existing designs

Why did the Implacable class remain close to treaty displacement if the Navy wanted a larger combined carrier?

Construction speed favoured adapting the armoured design already being built, while existing carriers and Ark Royal supplied strike capacity.

The Implacable design reflected the need to get ships into service quickly. The 1934 Design X had already explored a combined strike-and-battle carrier, and Audacious is identified as its later expression. Treaty limits had forced the Navy to divide those capabilities among different ships. Courageous and Glorious still supplied strike capacity, with Ark Royal reinforcing that group as Furious aged. Developing the armoured carrier design already under construction offered a faster route to more ships.