But actually, it isn't. Words akin to "gnome" appear all over Europe, but rarely do any two groups agree on what the darned things are. Similarly for "dwarves" and "elves". There's vague mappings between the mythological critters of various cultures, but they are only vague.
D&D stole some concepts from Tolkien, and Tolkien influenced pretty much every Engligh language fantasy writer after him. But don't for a minute mistake that for the idea that Tolkienesque elves and dwarves are really mythologically common.