It doesn’t matter as much as it used to, not by a long shot.
But the main reason is the increased selectivity over the past 20 years.
20 years ago, anyone could get in. So if the child of a legacy wanted to go, and they were willing to cut the tuition check, why not?
But it’s a different ballgame now. Most legacy parents, if they had to apply now with their grade and test scores, couldn’t get in. Neither can their kids.
But IMO if the applicant has competitive numbers, legacy is still a good “tip” in their favor.