As an Indian, I've learned from school the cliched "because we already had a culture" reply. Just how true is this statement? I'm talking about British individuals not the army people or gov servants. From what I've read, yea sure we didn't exactly love Englishmen, but to be certain there was little hostility so to speak?
It's not that they left, it's that they never came. The other countries you reference all had large British settler populations. They came, acquired land, and built economic livelihoods that weren't directly tied to the colonial administration or to British companies. By contrast, most Anglo-Indian families were employed in some way either by the colonial state or by the major European trading companies. There was never a big push for civilian British immigration to India, so when colonialism ended, most Anglo-Indian families left. 150k people is peanuts compared to the British settler population of Australia, for example - nearly 3 million Brits immigrated to Australia.
As a side question, how many British people were in India just before independence, and how did that compare with the numbers after? Did the majority of them do work for the Raj, or was there a significant presence of private citizens doing their own things?