An unguided torpedo is an uncertain weapon rather than an automatic kill. A target that detects a single salvo may turn away and open the geometry needed to escape it. Concentrating many tubes in one ship therefore offers less tactical gain than the raw number suggests. Distributing the launchers across several destroyers lets a force attack from different bearings, complicating the target's choices and making the salvo harder to dodge.
Notable Point · 1:20:18-1:20:58
Why multi-bearing torpedo salvos are harder to evade
A mass of torpedoes from one ship is easier to evade than coordinated attacks launched by several ships from different bearings.