There's definitely a genetic component to skinnyfat, but you're not doomed for life if you have it. I had it for a while, but I got rid of it with enough time and effort.
Low adipocyte count and possibly high T. Very lucky.
Some pro athletes carry more fat on purpose for specific reasons. A few fighters like having a protective layer around their midsection. A football linebacker benefits from more overall mass. For sumo wrestling, being fat is an essential part of the sport. Most athletes, however, prefer to stay at least somewhat lean.