Several reasons actually.
As someone already replied, cost of living is a fraction of other developed countries. In my estimation, it can be as much as 1/6th for frequent expenses like eating out. Housing costs in the bay area are a disaster. You can build a nice nest-egg and retire comfortably in India with that kind of salary. Travel the world when India becomes too much to bear.
If you do travel within India, you can stay in places that are super nice. Think of Taj hotels, CGHs, Oberoi etc. It would be impossible to find equivalent service in other countries.
Access to cheap physical labor: Ecom, quick, drivers, maids, nannies, cooks help free up a lot of time that you can spend on hobbies and working out.
At that salary level, you can live in a gated community and cut yourself off from real India. You can create your own substitutes for stuff that does not work: water, electricity, lack of open spaces.
There are not too many places in the world which are welcoming and have high-paying jobs. EU, ANZ, Canada just don't pay enough and have really high COL. Every other centre is hit and miss w.r.t acceptance of foreigners and quantum of jobs. That pretty much leaves only the US.
Plus there is an intangible benefit that you will feel genuinely well off in India at that salary level compared to your peers and definitely the rest of the country. With an equivalent job in Bay area, you will feel middle class at best.