@Nocreativity1 You’re correct that it’s not unique to Ivies. Ivies simply have the strongest effects of legacy. Of course places like Georgetown, Notre Dame, etc. all have legacy preferences. Weirdly, it seems that top LACs give a higher boost to athletes than to legacies. Probably because they’re smaller and their legacy pool is smaller, and do not have large graduates schools as an extra sources of legacies, as do Ivies or other selective research universities.
Still, Ivies have the strongest legacy preferences, even among the rest, since the entire legacy preference idea started in Dartmouth, and then was adopted by Princeton, and later by the other Ivies, as a way to reduce the entry of Jews, who were entering the Ivies in large numbers in the 1960s, much to the dismay of most of these universities.