Why did Gloucester-subclass cruisers carry larger crews?

Why did the Gloucester-subclass Town cruisers have larger complements?

They could carry more Royal Marines, had different accommodation, and needed a somewhat larger engine-room crew.

The Gloucester subgroup carried a larger complement because it could embark more Royal Marines and had different accommodation. Its machinery arrangement also required a somewhat larger engine-room crew. Those demands raised the total even within the same broad cruiser family. Crew figures reflect assigned people and technical systems as well as displacement.