Real world logic and video games, especially fantasy/sci-fi video games do not mix.
Blizzard has always put fun and gameplay ahead of lore and logic. There are guns, magic, and swords all in Warcraft because it gives the player more variety and fun that way. Limiting that just for the sake of realism was not something they wanted to do. There are plenty of other more realistic games out there, Warcraft has always had a pretty big dose of the absurd and silly mixed into it.