Why USS Olympia was unusually heavily armed

Why did USS Olympia carry guns more typical of an armored cruiser, and why were similar protected cruisers uncommon?

Olympia was a specialized long-range commerce cruiser designed for independent action, making her an expensive exception rather than a general pattern.

Olympia was a special-purpose ship rather than a model that every protected cruiser should follow. She was designed as a long-range commerce cruiser expected to operate independently. That mission justified a gun battery more often associated with larger armored cruisers. The cost and specialization that produced Olympia also explain why similar protected cruisers were uncommon.