Can you think of any other league in professional team sports that has successfully covered Europe and North America?
No other league has needed to try. All the other sports were already international. That’s why the NFL is trying to swim up this stream. They don’t have an Olympics spawning the game in other countries, they don’t have a FIFA (badly) overseeing the sport globally, they don’t have any kind of international competition inspiring the next generation of players. Heck even NASCAR can pull talent from around the globe because everybody races something. It might be an impossible task, but it’s a mountain they need to climb.