Though if I explore this further.
I think that when Sikhs were moving to New York in the 70's, it was a much rougher place than it is now.
Manhattan is like Central London and people mainly lived in apartments and in those days it was a much sleazier place.
Our people don't like living in apartments. We prefer houses. There is no way our people like to live in places like the Bronx (too many blacks), Brooklyn has too many blacks as well.
So the only borough that may be suitable is Queens as it was probably more affordable, less crime ridden where there is more space and you could buy a house. Not a terraced house but a detached one with a basement.
What you probably also note is that the demographics has probably changed.
These boroughs of New York are quite big and Richmond Hill probably more Jews and Italians living there and probably less blacks Hispanics etc
But over the years there has been a demographic shift. This might explain in part why we are seeing things happening. But there are likely also other factors.