The hype has worn off VinFast, with its stock spiraling lower since its IPO a little over a year ago. But why have investors been backing off recently?VinFast Auto (VFS -7.58%) was an intriguing investment from the get-go. At a time when investors are flipping over every rock to find the next Tesla, VinFast dominated its home Vietnam market, offered compelling cost advantages, and had state-of-the-art production facilities, and a very wealthy backer and founder. The electric vehicle (EV) maker also had exte ...