People found fossils for dinosaurs and created the idea of dragons because there was no actual concept of dinosaurs yet. The reason people all over the globe have their own versions of dragons is simply due to the fact that dinosaurs were spread across the globe.
But all dragons are pretty much the same, despite European ones. They had crazier versions such as 3 headed ones. Also, our ancient myths tell us that dragons existed while humans walked the earth. Although, you do make a point.