"How can one be so ruthless as to sever ties to their families for no reasons after they come to the US?"

It is the result of moral-less education, greedy people and the society that values  success only in monetary values and expensive tadakbhadak.

Many people in US have inferior complexity. They fear of being a role model of "failure" in life because they don't earn there as much as their families back home expect or feel proud of. That might have caused a kind of mental torture on them when they keep on touch regularly. The better way to avoid this torture is to cut off communication. 

My friend has a son in USA since last 10 years. He wants his son come back with 3-4 laakh dollar and live princly life in Nepal.  That is too much expectation. It is not possible to save 3-4 laakh dollar in 10 years in USA no matter how hard one works. His son went USA as a student, spent 2+5 years in study (masters + doctorate), came back to marry, took his wife to USA (wife not working there), working in postdoc position and raising a small kid. Probably he may have 1 laakh dollar saving, which is 70 lakh here in Nepal, not enough to buy a thikkako home + car. If I would be his son, how could I face his expectation?