Assimilation of immigrants

Why do people migrate? How often do people migrate because they absolutely hate their own culture and want to start fresh and take up someone else's culture. Start fresh. Not very often I presume. Even when someone wants to do that how likely is it that his circles of family, relatives, friends, and other acquaintances agree with him completely and will change to accommodate his new culture? That's what I thought too. 

We often talk about immigration and we complain how it would be so much easier if the immigrants were not as much stuck to their own culture and tried to adopt to the new place, new language, new culture, and new tradition. If only they learned English and spoke like normal people, some people say. Well, I agree in the case of kids and education. Kids who are young enough to start school in the US must go to school and their school must be in English. However, I am not so sure about adults though. Studies show that adults have a more difficult time learning a new language than kids do. This is a problem and makes it so much harder to attract immigrants to the US.