Is it indeed? Could you for a minute just think of the possibility that some fields that someone wanted to study or specialise in are not available in India?
That.. in order to obtain this expertise and bring it back to India, Indians must go to where it is taught or practised?
Look at all the top positions in premier Indian research institutes like NRSA, PRL, ATIRA, ISRO, TIFR...these are Indians who did their basic education in India but specialised in niche disciplines in universities in Europe, US, Canada.
Step out of India for a couple of months and you'll see that its not just in India... its a global phenomenon. Its called the "spread of knowledge". "Brain drain" is just a buzzword created by envious "i tried to go to phoren but I didnt make it".
The ones who made it... have not fled... they have gone to return with something better. Think about that...