this is like commenting code - who is the code meant to be written for? other programmers, or the compiler?

No, this is nothing like commenting code. These comments are not meant for other "programmers" (i.e. Justices). They're meant for the public, which doesn't compile anything with regard to the Supreme Court.

No, they're meant for other Justices, too, as well as for judges and lawyers beyond the Supreme Court. They're annotations describing the rationale for a decision - the "why" of the verdict - in as much detail as possible, which I reckon to be invaluable to anyone else needing to go back and evaluate that decision and determine its implications.

Sorry, still disagree. Contrast an opinion from Thomas or Breyer (or even Kennedy for that matter) with this one from Gorsuch. The quips and trite verbiage are absent. And for good reason: it's not serious, and it's something people latch on to instead of the legal text of the opinion, especially today in the world of twitter and memes. People like the idea of Ginsberg as a feminist icon because of her terse dissents and demeanor but that's actually really kind of terrible. This isn't her fault - her opinions are absent of this kind of flowery language. They're to the point and well written. So I guess my point is Gorsuch is just asking for it - to be a pop culture thing. We should not want this of the High Court.

>the "why" of the verdict

SCOTUS doesn't have "verdict[s]".

I'm not a lawyer but I've read probably 200+ opinions for fun over the last decade, listened to maybe 100+ oral arguments. I really love following the Court, and I probably have an allergic reaction to these people growing beyond their britches (they are unelected, after all).

Surely the public (ie. non-lawyers) are a vanishingly small proportion of the people who read beyond the syllabus?

If it makes more people interested in reading legal rulings - and in this case, realize that all of eastern Oklahoma belongs to the tribes - it's a good thing. Awareness is important in rulings like this. This ruling was necessary because a lot of people "forgot" that eastern Oklahoma was given to the tribes.