Now, there are certainly exceptions to this rule. Skyrealms of Jorune famously (one might even say infamously) presented a fantasy world that was almost completely alien. Tekumel, too, veered consciously away from the "classic" milieu mold. Runequest has its ducks. There are many other such examples (and when done to consciously differentiate themselves from the standard, fall into the "our monsters are different" trope).
Indeed, Tolkien's elves and dwarves do more than make an impression by their presence; their very nature harkens back to his work directly, which itself takes its inspiration from Norse and Anglo-Saxon mythology. The elves of Victorian myth were diminutive fairies only half in our material world. Dwarves were good for little more than hording gold and perhaps clever craft-work. Tolkien hearkened back to pre-Christian mythology and envisioned multiple, physical, races living alongside humans. And that basic model, more than the specifics of the races themselves, are the long shadow that is cast across most RPGs today.
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