Why battleship spotting aircraft remained biplanes

Why was Britain slow to adopt monoplanes as battleship spotting aircraft?

Because biplanes offered strong lift and easy takeoff, while a monoplane's extra speed brought little benefit to an aircraft flying local spotting patterns rather than long-range reconnaissance.

A gunfire-spotting aircraft has a different job from a reconnaissance aircraft. A battleship spotter needs to launch reliably, remain near the firing ship, and observe fall of shot. Greater speed adds little when the aircraft is flying repeated patterns over the fleet. Older aircraft technology could therefore remain well matched to this narrow naval mission.