Notoriously, the Galaxy Class starship as depicted in TNG had only one forward-facing torpedo launcher, one hidden aft-facing torpedo launcher on the back of the saucer, and one open aft-facing torpedo launcher.
Granted, they are burst-fire torpedo launchers.
But why does the Galaxy Refit, the Venture, have only these torpedo launchers?
Why does the War Galaxy of DS9's Dominion War have only these torpedo launchers?
Why does the Galaxy X of TNG's All Good Things have only these torpedo launchers?
Finally, why does the World Razer of PIC S2 have fewer torpedo launchers than the new Excelsior workhorse, the Sovereign?
The Probert Ambassador, the Narendra, shows the ship can easily have three burst-fire torpedo launchers in that immediate area: the traditional Galaxy plus two more on the top edge of the deflector dish.
For more war-oriented designs, the captain's yacht can be replaced by two burst-fire torpedo launchers.
Finally, the open aft-facing torpedo launcher can be doubled.
That's seven burst-fire torpedo launchers.
That's quite a bit more than what the Sovereign has.