Maybe it's the way past human cultures decided to explain dinosaur fossils, and the legends created out of random finds have endured to this day. Or maybe its some primal psychological throwback to when mammals were small furry snacks for lizards and the shape of a gigantic reptile as a symbol of fear and power is etched into our racial memory.
Anyways a bunch of cultures have traditions and myths dealing with dragon or dragon-like creatures, so they evidently evolved in parrallel. But then again so have things like worship of anthropomorphic spirits/gods or other fantastical creatures, and they don't exist either, as far as we can tell. Humans have too much of a weird imagination. We should totally get our genetic scientists on the ball figuring out how to custom create a real life friging dragon though, thatd be sweet.
