Whenever I see this argument about how good bows and swords are in modern warfare I am reminded of ‘Mad’ Jack Churchill, a British officer who fought throughout the entirety of World War II with a Longbow, a basket hilted Scottish sword, and Bagpipes, whose most infamous quote was “Any Officer who goes into battle without a sword is improperly dressed”. Apparently he both scared the hell out of, and supremely impressed the Germans, and was regarded as ‘unkillable’, to the extent that when SS troops had managed to take him and others prisoner, and were rumoured to be about to execute them, a regular German army unit rocked up saying they would turn their guns on the SS troops if they tried to. The SS promptly backed down and retreated, and the German troops just said “It wasn’t their place to keep such a man prisoner” and he ended up walking 150 miles to Verona where he rejoined Allied forces. What a lad…
Anyway, I think the way I tend to look at it is that Guns just aren’t the game changer on Azeroth that they are on Earth. They simply can’t be, as, as has been pointed out, if they -were- then everyone would be using them, however, to bear in mind is the fact that using the example of ‘Mad Jack’ there, in the hands of a skilled archer, a Longbow is every bit, if not more, deadly than a firearm, for races like Kaldorei and Sin’dorei, both of whom culturally are well known for their archers, it makes sense that whilst they know how guns work, and can make them, they still likely favour bows. The Elven ranger with their bow is an enduring stereotype after all.
Whether this is because Azeroth’s inhabitants really are ‘tougher’ than humans in our world, or because armour is more effective (doesn’t really explain cloth armour though)or simply whether guns are as -powerful- as in our world is up for debate, but what does seem to be the case is that guns are used chiefly by those species to whom it is a cultural imperative, such as Gnomes, Dwarves, Gilneans, Kul Tirans, Goblins and to a lesser extent, humans and Forsaken, The other races have people with guns, sure, but aren’t as culturally associated with them, and moreover, don’t seem to suffer from not using them en masse.
Way I personally look at it is the “Guns simply aren’t all that and a bag of chips” argument. They’re nothing special, just another weapon, not powerful enough to revolutionise warfare, but powerful enough to be a viable tool of war, so it really is just a question of culture and aesthetics,as to whether they are used.