there are a number of reasons why djokovic keeps winning and dominating.
he is constantly bringing in experts to help him improve his game and his fitness. so he is outworking them all.
another reason is a bit of a luck: his main rivals are not getting near him.
roger is just too old and andy has no forehand. andy will need one hell of a match and djokovic would have to a little bit off.
but I don't know if djokovic will be off. he is working on his game night and day to be that sharp.
and rafa is just not interested. he is not interested in making the slightest change in his game, his fitness, and his physical work in the gym.
that London O2 arena match at the end of the year and the Doha final showed very clearly that the gulf between djokovic and rafa is greater than ever.
Rafa is practicing on clay now but that is no enough. he has to fix his fitness and start doing some very serious physical work in the gym.
pros who are the ultimate insiders of the sport say he has very little endurance and also has lost substantial amount of muscle mass.
of course it is not rocket science. we can all see that too.