That’s really interesting. It also fits with the fact that the flagships of the states that consider legacies are all within the list of public school to which the top 1% send their kids (https://www.nytimes.com/interactive/2017/01/18/upshot/some-colleges-have-more-students-from-the-top-1-percent-than-the-bottom-60.html).
Interestingly, though, even states which have no legacy preference have a very large proportion of the richest kids in their flagship universities, like UIUC, Arizona, California, and some others. Then again, unless you’re looking at Engineering, acceptance to UIUC for a kid with a decent GPA and SAT score is not difficult, and these are easy enough to achieve for an average student with good financial resources, but extremely difficult for an average student who is also lower middle class or poorer. Also, Illinois has a large number of cheaper public universities, as does California.