Nadal did not play in India because his wrist is bothering him again.
This guy just does not learn. Why the heck go and play in freaking India some meaningless tie?
Every headline I've seen lists 'stomach upset' as the cause for Nadal not playing. I think he hopes to play a match on Sunday.
As for why he'd play in the first place, it's always good to get a relatively high pressure B05 match in when trying to get back in good form on tour especially when you haven't played a ton recently. And before someone tries to point out that beating the Indian team shouldn't be high pressure, 'pressure' in this case is obviously not from the opponent but rather from the stakes.