Why don't they just support the growth of their own homegrown "WhatsApp"?

With government support and financial support, india could easily have an indian "whatsapp". WhatsApp isn't technological sophisticated. It's simply a large network. With government/business "tweaking", india could help their own "whatsapp" company take over much of that market from facebook.

Why hand the entire indian market over to facebook and zuckerburg?

There is no reason why large and significant markets shouldn't be dominated by local businesses. Not to say whatsapp should be banned from india, but it's only the incompetence of government/business that cedes their market to foreign companies. This also applies to the EU. It's insane to me that the EU doesn't have their own google, facebook, etc.