If you dedicate years to honing your Starcraft 2 skills, but consumer interest shifts to Overwatch or Destiny, can you retrain fast enough to compete at a similarly high level?
In IRL sports, the rules of a specific game don't change. Neither does the size of the field, the goalposts, the ball itself. So as long as you're able to improve your physical/mental focus, you can improve your performance. That's not the case when multiple variables around the game itself are changing.