Why? He just got a week's rest and has at least a week rest after Miami. Besides, his game is suitable for these courts I guess.
He's old, his body is fragile, his ankle had to be thoroughly taped in IW. After his heavy February schedule he developed left knee tendinitis on top of the recurring wrist problem. Hard courts are his weakest surface and hardest on the joints. I mean he lost 7 matches in a row before the South American clay swing (all on hard courts). If he wants to prolong his career, he should try to avoid them as much as possible, sticking to softer surfaces.
But obviously it's up to him, if he enjoys competing at all the big events, so be it.