Probably because Fed was good at exposing his bad movement last year. Still, I feel he has made strides in that department. If that will be enough remains to be seen.
Fed is also very smart in terms of reading the play, and seemingly isn't bothered that much by junkballing/constant changes of pace. Those are Tomic's biggest strengths.
I think Tomic will probably hold a respectable number of service games, but will struggle to get a look-in at breaking Fed. So we will probably have 3 or possibly 4 close sets without the ultimate result ever being in serious doubt.