I want to make a few more points.
Sacrilege – you don’t think that the unwillingness to leave family/friends is a reflection of immaturity. Perhaps I labeled it too quickly but I think it is due to either immaturity or inflexibility/being set in one’s ways and afraid of change. The Torah tells us that a man has to leave his father and mother when he gets married and cling to his wife. Some people are afraid to move further than around the corner from their parents. Part of the maturity that is necessary to get married means leaving one’s parents, as terrible as that sounds. I don’t mean to abandon them. I have many friends who made aliya and whose parents eventually followed them. I don’t mean to leave behind a sick, elderly dying parent, but if a couple makes aliya when their parents are still in good health, they can certainly join their children there. My mother-in-law came in her late 60s; I know people who came in their 80s and even 90s. On the other hand, I think that some people don’t want to leave their parents, relatives, friends, etc. because they are simply too set in their ways – almost like over the hill, “overmature” rather than immature. Familiarity is too comfortable for them. Even if their situations aren’t so comfortable, the familiar known is less threatening than the unknown.
Another important point to think about – since I’m female and don’t learn Gemara I can’t quote you Masechta and daf, but there is a famous Gemara that says that three things are acquired only through yisurim – Torah, Eretz Yisrael and Olam Haba (I don’t know if they are listed in this order). Everyone always quotes this gemara as an excuse not to move to Eretz Yisrael because it is acquired through yisurim. Well, let me ask you all to think about this honestly – don’t we try our best to observe/learn Torah and to do mitzvos to acquire Olam Haba, even though the Gemara says they are acquired through yisurim? Why are we only afraid of the yisurim of Eretz Yisrael and not the yisurim involved in acquiring Torah and Olam Haba? Why do we seem to view Torah and Olam Haba as obligatory, despite the yisurim, and Eretz Yisrael as optional?