1- This is boldly assuming they're trying to bring in immigrants. They likely will, but they're also not nearly as concerned about getting those people visas because if you can't get a visa, they can just select from other elite candidates who can.
2- There's also plenty of bad things about Bangalore, like the fact that the infrastructure isn't nearly as established as NYC.
3- NYC offers immediate proximity to one of the nerve centers of global commerce. There are hundreds of major multinationals based there, and that proximity is valuable.
4- The US has the 3rd largest population behind China/India, so it's not like they're lacking in bodies to fill roles. The size of the population and the size of the economy aren't the same thing (India's GDP is currently 1/10th of the US's, despite having more humans living there).
1 - My idea of a starting headquarters in a country which dont have much VISA issues was to help hire more diverse pool of candidates which is not limited to the US citizens/people studied in USA.They can also do internal company transfers but these things are mostly for people who are really good at politics or that is what I heard.
2 - Yup. But people from India and Indian subcontinent are used to these things.
3 - I mean Amazon already have a US headquarters.
4 - Yup. Indian economy is currently lagging behind USA. But its still a huge economy. Maybe Amazons 2nd biggest userbase after USA and its heavily growing.