Whole lot of turrets launching swarms of Trebuchet-esque missiles would work way better than torpedo launchers. Torpedoes (or heavy missiles like Helios and Cyclops) need to be delivered by bombers to have any effect against a capital ship protected with blob and flak turrets. Even then, if they are released too early, they will be wasted before doing any real damage.
So, I would guess that they've tried that and noticed that launching torpedoes from capital ship to capital ship was not only complete waste of money in munitions, but also waste of space for some other type of turret.
Obviously, if they develop an armoured torpedo (
@concept) they can use it to penetrate flak and blob barrage and to get it to hit the enemy ship's hull...
Realistically, I would rely on projectile weapons, though. And of course any spaceship's engines could always function as weapons too. I have always thought that the engine wash should really
cause massive damage to systems of any poor bugger who decides to fly behind engines that can move several kilometres long ships. And it should effect longer behind the ships. I'm not talking about mild rumbling that slowly washes shields away and disrupts targeting. I'm talking about being vaporized, annihilated and blown to kingdom come in seconds for fighter-sized objects.