Why the Calypso class stopped after two ships

Why did the Royal Navy build only two Calypso-class corvettes?

Because many earlier ships and classes could still perform the same station and presence duties, so the Navy did not need a large run of this one design.

The Calypso class did not represent the Navy's only investment in this type of small cruiser or corvette. A succession of preceding classes and individual ships remained available for similar work. Station vessels served as gunboats and visible reminders that heavier forces could follow, a role that did not always require the latest speed. Looking at one class in isolation therefore understates the number of hulls available for imperial presence and patrol.