Originally Posted by NLBwell
I believe that in general, guys who grind out every point and reach the top burn out mentally and their bodies start to break down quickly. Borg, Wilander, Courier, and possibly Nadal fit into that mold. Nadal's extended break here could lengthen his career, as it lets him rejuvenate mentally as well as physically. We'll see.
I think this is the closest answer to the real reason.
A Wilander type player, see Borg, Courier, Chang.
You just hit a wall one day and that's it!
Best comparison is a boxer, one day it's just not there anymore, for a number of reasons.