Winning is always fun, who could ever get to the point of not enjoying it?
Sure it is but it's not always that fun to win by, say, 2 minutes. It's more fun to win a well fought race than it is to run away from everyone. Running away from the competition can definitely feel like a hollow victory. I've been in some races where it didn't even really feel like a race because I didn't even see anyone after the second step and didn't have anyone near me after 50 yards.