20% of Americans are Catholic, but 5 of the current 8 Supreme Court justices are, and Amy Coney Barrett will make it 6 of 9, fully 2/3 of the Court.
Why this oddity? My guess is the abortion issue. Only one of the Catholic justices was appointed by a Democrat, Sotomayor, and that appointment was to try to bind Latinos to the Democratic Party by putting the first Latino on the Court. The other four were all by Republican presidents, who, whatever they personally think about the issue, find political advantage in playing to the pro-life constituency.
So why not appoint pro-life evangelical Protestants? This is just a guess, but they tend to be more openly in-your-face about religion as culture war than most American Catholics, in a way that most of the leadership of the Republican Party, which tends towards mainline Protestantism, is not comfortable with.
Those folks do well in state and local politics, but less well on the national stage. The Christian Coalition had its heyday, then sort of burned out. Nominating someone from that crew would probably get a surer vote to overturn Roe, but would likely face stronger opposition because of their general religious triumphalism.
Here's where I am being serious, but keep in mind this is pure speculation, so take what I am about to say for what it's worth.
In Larry Seidentop's book "Inventing the Individual," he points out how the Catholic Church essentially becomes a church of jurists and lawyers following the reforms of one of the popes (I think it was a Leo, but not sure. Going off memory here). In an effort to standardize canon law, much theological education became about studying various systems of law. To this day, Catholic education focuses on close study of texts.
So, perhaps, this Catholic culture of close studying of texts and differing legal systems has a tendency to produce jurists, even among laymen?