The 57 Chev was so popular so long for a couple of reasons. The55-57 series was the first with a V8, making them easy to hop up. The 58 and newer models were larger and heavier making them less desirable for performance. Of the most desirable for hop ups, the 57 was the newest. So it was a combination of things that made them desirable, and once they got the name for being "cool" it stuck, even among people who know little about cars and hot rods.