Why aircraft did not replace cruisers

Were aircraft replacing cruisers in the reconnaissance role?

Not at this stage. Aircraft covered wide areas quickly, while cruisers provided persistent all-weather presence; the two worked best together.

Aircraft carried by cruisers expanded their reconnaissance reach, but interwar aviation could not maintain an all-weather, around-the-clock presence everywhere a cruiser might operate. Night, storms, distance from airfields, and the absence of a nearby carrier all limited aviation during the 1920s and 1930s, with some limitations persisting through the Second World War. Ships and aircraft therefore filled complementary roles. Aircraft search wide areas quickly, while a seaworthy surface vessel remains on station for persistent monitoring and visible presence. Because sea control cannot be fixed in place like a wall, that presence is always transitory and must be renewed by ships and aircraft operating together. A modern island-security example calls for about four P-8 maritime patrol aircraft, backed by UAVs, fighters, offshore patrol vessels, and a surface escort. Cruiser-like persistence still mattered for diplomacy, deterrence, fisheries protection, and wartime action.