If SCOTUS can upend decades of precedent to eliminate race-based selection, then certainly the courts and the schools can see how legacy preference – which overwhelmingly favors white applicants and gives a leg up to the wealthy over people from marginalized communities – should be abolished. Legacy preference is a large part of structural racism in the US.
Legacy preference in college admissions is necessary for the survival of the institutions that use them. Not only are legacy applicants more likely to enroll in the school – making for a smooth and certain admissions process — but they're also more likely to become donors who contribute to the endowments that keep private schools afloat. Whereas affirmative action had little benefit to schools, legacy preference is a school's lifeblood.