nalbandian said this but we said it long ago:
it is clay or the exit.
clay is the wellspring from which he flows. he has to be able to run over them on clay in order to do well against them on other surfaces.
he has 46 clay titles. that should spell it out clearly.
clay gives him the consistency, momentum, and the confidence.
but he is not young anymore. the youth is gone.
so now he has to work harder than ever before and he simply refuses to do that.
for him to dominate them on clay, he has to have supreme fitness and superb physicality. he wont put in the required time to get that back. he just does not want to.