Why protected cruisers did not make torpedoes their main weapon

Did anyone design a protected cruiser with torpedoes as its primary weapon?

Not really. Contemporary torpedoes were shorter-ranged than the guns a cruiser could carry, so they were poorly suited to be its principal armament.

Torpedoes of the period did not offer the reach expected from a cruising warship's principal weapon. Guns could engage at longer range and therefore better matched a cruiser's need to threaten, pursue, or disengage from varied opponents. Torpedoes remained useful secondary weapons for favorable close encounters, but making them primary would force the cruiser to enter a tactically restrictive envelope. A cruising ship's main battery needed the longest useful engagement range it could sustain.