I’ve been saying this for years.
In the academy, it’s always considered bad form to hire your own doctoral students into your tenure track. It’s also considered poor form to hire the majority of your faculty out of the same program. Diversity (up to a point) has long been recognized as a positive thing in academic disciplines.
The Supreme Court of the United States isn’t dominated by the Ivy League: it’s dominated by two schools in the Ivy League. Harvard and Yale. Right now, the only Justice not affiliated with Harvard or Yale is the Handmaid, and she went to Notre Dame. These people do the legal equivalent of post-doctoral fellowships at the Supreme Court and/or the DC Court of Appeals. They are in the chambers of judges who went to the same schools they themselves attended.
Law school and clerkships are where people learn to think about the law as an intellectual discipline. These people are only exposed to a couple of ways of thinking that way. It’s not a good thing.