Also, it happens that only one torpedo is needed to kill the target and this is often the case in Wing Commander.
Firing two torpedoes when you can use one is pointless, not to mention that even if one torpedo won't kill the target, it can still weaken it, so you may kill it with guns and normal missiles.
Okay, thanks for the replies. I just remember firing 4 FOF's into the face of a Vaktoth once and with the Avenger in WC4 I love the ability to fire all torpedo in one salvo. That was how I took down the Lexington. At least it is not the one torp at a time thing like in WC2 and Prophecy. That was a pain in the rear.
The first one was quite pointless, considering that 2 FOFs and a gun salvo should reduce the Vaktoth to scrap.
Lexington goes down after a hit with one or two torpedoes, there's no need to fire all of them.
Two torpedoes at a time would be enough, as multi firing only makes sense with DF missiles and even with them it's not a nessesary tactic, usefull mostly against warships.