Emigration to another country is an intrinsically egoistic act. Leaving family and friends behind, separating children from their classmates and grand parents just to accomplish one's own goals. Unsocial and egoistic. (I am excepting those, of course, who are emigrating to save their lives.) For people from poor countries it is often the only way to get ahead, but for those from well-developed countries it is an all the more individualistic act.
Egoism alone is not a problem. It is a natural part of human character and live. But if you have a regular instream of egoists into one country (all leaving their social networks behind), then it's no wonder that this country creates a very individualistic and less social culture.