Why HMS Hermes retained heavy secondary guns

Why did HMS Hermes retain heavy secondary guns until her loss?

Because her patrol duties could leave her far from cruiser support and exposed to a surface raider, so the guns gave her a measure of self-defence.

Hermes's armament reflected how early carriers were employed. The ship often undertook presence missions or anti-surface-raider patrols across a very large search area. Those duties could separate the carrier from accompanying cruisers by a considerable distance. Heavy secondary guns were therefore insurance against a raider getting close before support could arrive, reflecting an operating concept in which a carrier might have to defend itself against a surface ship.