Fun fact: the Edda (the collection of old poems that is the source of most of our knowledge about norse mythology) never actually says that dwarves are short. Quite the opposite: the only place I know that actually mention a dwarf's height describes him as gigantic, so large that he barely fits inside a king's great hall. Even Thor himself makes a remark that basically translates to "Man, that's one big-ass dwarf".
I have no idea why dwarves went on to become synonymous with shortness, though.
I have no idea why dwarves went on to become synonymous with shortness, though.
Same reason they became associated with Scottish accents despite being of Scandinavian origin and having a language based on Hebrew in Tolkien. What that reason is, is a mystery, but its gotta be the same cause.
Probably something to do with how they've become comic relief in most fantasy settings.