El Dude said:
Combination of things, some of which were on purpose. He voluntarily took pace of his fh and put a bit more spin on it, to try to beat Rafa at the french back in 2007. The fh was never quite the same after the AO 2007, especially after Higueras started tweaking it.
In 2008 he lost a half step (mono, lack of practise etc) and that was when he started getting the shanks. He was able to adjust to his new movement and get some control over the shanks but he never really went back to the way he used to hit the ball. I think he probably lost another half step somewhere between 2010 and 2013, and that definitely didn't help.
I mean its hard to hit a perfect inside out at full blast unless you really are comfortably in position, but i'd say its more than that. Federer simply chooses not to hit the ball as hard as he can imo.
There is another factor too, which is probably that balls are a little heavier than they were in the old days. I suspect that probably has a psychological effect, and forces the player to perhaps not hit as hard or as flat, since there is less chance of hitting a pure winner.
