Yup, i really do not get why ammo is so limited to missiles and torpedoes since they actually have countermeasures with PD and ECM. Sure, perhaps PD and ECM needs to be better but you cannot jam or shoot down an incoming artillery shell.
But you can shoot down incoming missiles. The patriot is an anti-missile missile. Basically a missile designed to destroy other missiles. And there is the phalanx CIWS, a 20mm minigun designed to take out missiles as well. both weapon systems have been in use by the U.S. military since the 1980s. In theory, the same holds for artillery shells. The thing is that neither of these systems are very portable. And there is the Boeing YAL-1. It is a 747 with a high-powered laser. The laser is designed to shoot down ICBMs.
We have the technology for this stuff right now.
Ammo is limmited on missiles and torps is because they take up considerable volume. Simply put: they are bigger than the ammo for pretty much any other weapon of the same size. Notice the difference between a class 1 and class 2 missile rack. The class 2 doesn't do any extra damage. Instead, it has more ammo to work with.
And the ECM isn't the counter it used to be. Its a soft counter. It can buy you some time from a guided missile or torp. It can interrupt the target lock for a few seconds, . PDTs are the only hard counter.